[2020] Inceneration plants suddenly not working + other issues

It could be a mod affecting things, or you could be hitting the vehicle limit. Those are the two things that come to mind at least.

Easiest way to have a look at all your mods is if you upload your output log (player.log on Mac and Linux) somewhere and drop a link here. This guide explains where to find it and suggests some sites to upload it to, since we can't attach files here on Steam.

https://steamcommunity.com/sharedfiles/filedetails/?id=463645931&searchtext=log

To check the vehicle limit, you can add the CSL Show More Limits mod and see how close to the vehicle limit your city is.

I don't see any mods that should be causing this. Real Time is the only one that does anything to the AI, but even then I would be surprised if it was the cause.

I would definitely get CSL Show More Limits and check how close you are to the vehicle limit.

If you aren't anywhere close to it, go to Content Manager, into Saves and find the save where this happens. Then upload it to the workshop and share the link to it here.

Efficient public transport to keep citizens from using cars as much as possible helps reduce vehicles in use.

You will also want to make sure that industry has more efficient ways to move goods and raw materials around. Cargo train stations connecting areas, and connecting to larger commercial areas, helps get trucks off the roads. Cargo harbors and airports (If you have Industries) also work for more efficient transport out of your city.

You can also use the mod Clunk linked, but make sure to read the mod description. It's also important to know, that once used you cannot remove that mod from the city again. That means, should it ever break, your city will be lost. Hopefully that won't happen, but it's important to know the risk is there and decide if you can live with it. :)