@RareAle Yeah I 100% agree the current situation stinks. I lost three pets irl last year and I'm in no mood to see suffering animals in Sims 4, not counting at a Vet Clinic where at least you have an effective way to help them. Unless this is fixed in some future game patch the Wellness treats and mods are all we have for a remedy.
I can't post links to mod sites here but you should have no problems finding LittleMsSam's Mods page. The mod I use is called No Sick, Dirty, Sad and Hungry Cats & Dogs (NPCs). It's a very small (20 kb) and simple mod that only does this one thing. For the most part it does not require any in-game menu commands, you just place it in your Sims 4 Mods folder and it works autonomously. A detailed description is available on the LMS download page. This mod will not affect any sick animal patients at a Vet Clinic if you are playing one of those in your game. Your household pets may still get sick during normal game-play and this mod will not affect that either.
LittleMsSam is very good about posting mod statuses and updates after each Sims 4 Game Patch so patch days are no real chore for me. There are a few other pet-related mods available there that you might also be interested in checking out, including an anti-fear training mod that allows you to train cats and dogs to no longer fear stereos, TV's, computers, etc. It drives me crazy to have a large pet dog spend half of it's day whimpering in fear over every electronic device my Sim uses! The mod will allow you to train them out of those fears over time.
MCCC is a massive mod that does many cool things. The MC Command Center .package and .ts4script files combined are over 1 MB and that's not counting any of the add-on modules. I love using this mod in other ways but it is definitely over-kill if all you are looking for is no more sick stray animals. Plus apparently you would have to manually click on each stray pet you want to fix. Tbh I have never tried using it this way as I no longer even see sick stray animals in my game because of the LMS mod.
Btw- I use both of these mods and they do not conflict so that's also an option.
Good luck, I hope this helps!