Regarding the Current Fitness System

Product: The Sims 4
Platform:Xbox Series X
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.77
What expansions, game packs, and stuff packs do you have installed? Basement Treasures Kit, Bathroom Clutter Kit, Bust the Dust Kit, Cool Kitchen Stuff, Desert Luxe Kit, Dine Out, Discover University, Dream Home Decorator, Everyday Clutter Kit, Fitness Stuff, Get to Work, Greenhouse Haven Kit, Laundry Day Stuff, Luxury Party Stuff, Movie Hangout Stuff, Perfect Patio Stuff, Realm of Magic, Romantic Garden Stuff, Seasons, Simtimates Collection Kit, Spa Day, Throwback Fit Kit, Vampires, and Vintage Glamour Stuff.
Steps: How can we find the bug ourselves? Correcting broken values / references and assigning values to blanks.
What happens when the bug occurs? The primary issue is that the Get Fit and Lose Weight resolutions never complete under any circumstances, whether by potions, serums, or exercise. The secondary issue is that most food items have zero calories and the cardio exercises don't have enough differences in value to be relevant.
What do you expect to see? Resolutions complete properly and healthy / unhealthy lifestyles having appropriate rewards / penalties respectively.
Have you installed any customization with the game, e.g. Custom Content or Mods? On console - never used.
Did this issue appear after a specific patch or change you made to your system? Neutral/Not Sure 

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As many players are aware, Sims do not passively burn calories during their daily lives and must commit to exercises such as jogging, swimming, running on a treadmill, playing the dance exercise on the television, skating / roller skating, or practicing yoga in order to prevent their meals from accumulating in weight.  I'm not on PC and nobody, not even Carl, has taken the time to get technical and dig into the code outside of one Reddit user making a Google Document and an accompanying Spreadsheet listing the calorie values for foods across the base game and whatever downloadable content was available at the time.

I've experimented with finding the most potent cardio exercise for burning calories and it seems that the treadmill is hands-down the best tool for the job, though only by virtue of having an exercise option made available through the Fitness Skill that allows a Sim to exercise for approximately two hours - rather than one - before receiving the Good Workout moodlet and being ejected from the treadmill.  While I do believe the No Sweat Run does burn less calories than Workout, Endurance Run, and Hill Challenge, the difference is almost negligible despite the description implying a higher disparity and, likewise, the other three options are almost identical in values with Endurance Run being the practical choice due to the added exercise time.  I've concluded that the optimal exercise routine starts with an Endurance Run on the treadmill, pushing the limits with the Hill Challenge until your Sim becomes too uncomfortable to continue, and then following up with the Dance Video exercise on a television - as it presently doesn't check correctly for the Pulled Muscle moodlet or a Sim's level of overall discomfort - or the indefinite Practice Yoga option before the Sim becomes able to get back on the treadmill again.  For this test, I used Sims that have essentially become immortal through reward traits with absolutely no cheats involved.  I'm a completionist and have been on and off trying to, "Complete," The Sims 4 over the last couple of years.

In regards to calories, a lot of foods are missing values entirely and have been totally forgotten.  Paradoxically, a lot of unhealthy junk foods - especially those related to the Baking Skill where the introductory message for the skill says, "Expanding waistlines" - have zero calories and, at worst, give you the Unbalanced Meals moodlet for +1 Uncomfortable mood after eating six consecutive servings.  The junk foods and desserts that actually have calorie values are honestly not punishing enough when compared to healthy foods, nor are they really rewarding in terms of influence over moods.  For reference, a Sim gains 1 pound for every 150 calories.  The most punishing food is Lobster Thermidor, with 800 calories per serving.  All of the base-game cakes are 500 calories per serving, all pizzas are 500 calories per serving, most bar drinks are 200 calories each, a bowl of chips is also 200 calories, Mac & Cheese is 200 calories per serving, Spaghetti is 300 calories per serving, and a Garden Salad is 50 calories per serving.  If a food item does not produce the Unbalanced Meals moodlet when eaten consecutively, or removes the moodlet when consumed, it's considered a healthy food by the game.  Perhaps the developers assigned these original values as a way of accounting for carbohydrates in traditionally high-carb foods, such as dishes that use pasta, but that's only speculation on my part and, were that the case, even the base-game junk foods should've been more calorie rich with lower hunger satisfaction to reflect the bad or empty carbohydrates that are in real junk food.  During the 2013 Gamescom Create-a-Sim demo, Jill Johnson said that being a couch potato and munching donuts would spoil your Sim's hard work on the weight machine, but muscle loss is just on a timer and foods like donuts actually don't have any calories.

One last thing:  Mod creators and regular PC users, including some within these forums, have already fixed the bug in The Sims 4: Seasons that causes the Get Fit and Lose Weight resolutions to not complete, despite rigorous exercise and a dream diet of zero-calorie sweets taking a maximum weight Sim to minimum weight - or lethargic to bodybuilder - anywhere within the seven-day window, though the issue still persists on unmodified PC, Xbox, and PlayStation copies.  I suspect the developers are aware of this, but haven't really bothered doing so much as copying the community's homework to fix the problem, as failing these resolutions only ever rewards your Sim with a Confident moodlet now instead of a Sad moodlet.  The way it was described is that there's simply an incorrect set value or reference that only needs a slight tweak to fix the problem but, again, I don't have a PC copy to take a peek under the hood with, so take this with a grain of salt.

In conclusion, with The Sims 4 team giving the game more quality-of-life enhancements and gameplay overhauls, I think the fitness system is also due for a rework.  Calorie values for all available foods, complete with a re-balance and trade-off between higher calories and stronger moodlets for junk and desserts; greater weight loss and muscle gain for more intense exercises; muscle loss penalties for lazier lifestyles; and a small passive calorie loss or gain depending on your Sim's lifestyle and traits - Such as Active versus Lazy - would make for a good start.