What Should I Do: SOLVED

I use a combination of two mods to help with sim autonomy problems in the game.

The first is Turbodrivers simulation unclogger, which can help with problems wherein sims are locking up in a frozen state. Available here.
And coolspear's Quicker Sim Autonomy & Simulation Lag Improvements, which just tweaks tuning related to autonomy for a smoother overall autonomy experience. Available here.

Both mods still work with the most recent update without any issues and are fully compatible with each other. Using them both, I usually have no simulation lag in my game even with maximum sims on lot set to 50 in MCCC and on the largest lots. (I say usually, because I had a little bit in a 64 x 64 lot with a TON of skill and entertainment objects after I had placed 2 copies of every single skill book on the floor. Until NPC sims had put away most of the books into bookshelves, that lot lagged a bit... :lol:)

That said, I voted for moving to a smaller lot. I find 64 x 64 just to be much too large for a played sim household. It's too big to feel cozy and homey...not to mention you can put, literally, everything you could ever desire on the lot, and I prefer to have incentive to visit other locations. My sims travel to "do things" pretty much every day, and I enjoy that.

Try deleting the cache and a Repair Game in Origin, just in case that helps.
Then definitely consider how attached you are to the current lot because a smaller lot is liable to lag less (depending what the issue is; for example, in Brindleton Bay the lag may be related to the stray pets running around...)

You could try...
1. Deleting randomly generated sims.
2. Deleting some items on the lot that your sims aren't using.
3. If it's a full house, move some sims out to another lot, and rotate between the households. Assuming that's allowed with the challenge.
4. Clearing cache files

If all else fails, move to a smaller lot.

Make sure you don't have too much in your sims' personal inventories and also in the household inventory. Not many simmers know this, but this one plays a serious role in lagging.

I play on the same lot and putting the game in windowed mode worked wonders for my lag.

honestly idk cause i have lag no matter what i do and this started with last update before that everything ran smooth with ultra *sighs*

I'll second @BoergeAarg61 Change your graphics settings. My old computer lagged massively and lot size had no impact, at least in my case. If my sim went to say the square in San Myshuno outside Waterside Warble things would be ok until a ton of sims started showing up. Similar thing with zooming out. If I pulled the camera back for a wider shot it would lag a bit or if I tilted it down so that it looked like I was at eye level with them. I hated to do it but I had to run the game at lower resolutions if I wanted to keep the detail level high on my sims themselves.

In addition to everything said before, lot size is less a problem than the built upon space on that lot, clutter, lamps and doors. Try de-cluttering your lot and see if that helps, and maybe merge some smaller rooms into larger ones.

I had a big family living in a huge house on that 64x64 lot in Brindleton. I "solved" the problem by paring my household down to just three sims, but that's not a good option for your challenge. I do wonder if it's the size of the lot or if the amount of furnishings in your house that's causing the problem, though. Your castle is beautifully decorated and full of fun stuff to do, but all those options mean more processing time. If your sims are rich enough, consider buying a retail lot and using it as a second home. Only use the residence for screenshots, or activities that can't be done away from home.

This really sounds like a computer hardware problem to me. Maybe you don't have enough memory, or you're using an older, slower processor?

You could try turning down the resolution to see if that helps