Without the "Unoffical Code Patch" this game can't be played with a bigger galaxy later in the game. You have 10 to 15 minutes between each turn. On an Ryzen 9 7950X3D!

With the Patch it get's better and you can play longer but after a while you still get the same problem. It get's worse and worse until you come to a point, where you don't get into a new turn. It just hangs (went to sleep and turn was not finished the next day). Neither reboot or disabling all mods helped with that.

It's true the Unofficial Code Patch does improve turn processing time over vanilla along with a few other performance issues. Albeit there are a few reports from people with relatively new hardware getting unusually long load time of 10+ minutes between turns. I'm playing on an older Intel Core i5-655K and it takes me no longer than a couple of minutes to process a turn on a large galaxy past turn 500. Unfortunately I have no ideas what the culprit could be. Perhaps it could be identified by trying disabling non-critical hardware features, dual-booting from a different OS or, if available, testing running the game on another computer.

There's also a separate infamous softlock issue that will cause the turn process to never complete. If that happens there is a risk of that saved game already being irreparabel. According to the patch author WhatIsSol, based on read output logs from various reports, the most common causes are due to UCP being improperly installed, incorrect mod load order or mods that simply are incompatible with each other. Also avoid arbitrarily disabling/enabling mods mid-game because that is just going to make everything even more unstable.