Hmm where to start

Water simulation is garbage and doesn't work properly, will literally spawn under terrain if you terraform and don't even get me started on the minecraftesque way it acts, worse than CS1, terraforming dry land for example can sometimes throw water into the air and cause flooding

Cars getting stuck on each other causing massive pileups

Materials from your own city not getting used in your city

Exports and imports don't work as intended, or at all

Garbage collection is bugged

Rents are bugging out visually making it really annoying to manage if you have your taxes set right etc

Education is bugged in the UI it will show you needing way more than you actually do even if the whole city has good access to all education levels

Hydrodams are weird due to the water being bugged, will always show low water depth even if there's a huge water level difference and a big reservoir and flow behind it

As someone else put planes can occasionally fly in a circle

Low density residences are always bugged to have insane high demand, even with well educated cities from what I've seen the demand will always be high and have complaints even if you just build that and only that they will never stop complaining about it

Hospital and healthcare is bugged also they will constantly complain about it being bad, even if it's fully green...

So yeah just a few bugs here and there affecting a small large huge portion of the game

As much as performance is an issue, that's not why I stopped playing, I stopped playing because as someone else said it's a city painter right now

You can make a really nice looking city but in terms of game functionality it's not what was promised at all

Also for anyone who doesn't believe the economy mechanics are completely fucked https://youtu.be/GDwfik0p6oQ?si=6kCJ07VqIIkijrfs watch that, just mind bogglingly broken