[2021] Loading screen stuck loading

Sounds like maybe a simulation error. I recommend adding these two mods:

https://steamcommunity.com/sharedfiles/filedetails/?id=529129546
https://steamcommunity.com/sharedfiles/filedetails/?id=1620588636

Then before loading your save, go into Options and find the Loading Screen Mod. Find the Safe Mode options and enable them. Then try loading your save.

If that does the trick, save as a new file and remove the above mods again.

If it doesn't work, we'll need to look at your output_log.txt, which you can't attach here. In that case I recommend posting on our official support forum:
https://forum.paradoxplaza.com/forum/forums/support-bug-reports.879/