Happened to me too, here's the latest save file:
https://fastupload.io/85e99d927fc831e7
I play as Humans, joined Freedom Alliance, defeated Shakturi, and then captured all other civilizations (including my ex-allies). While capturing, I apparently found a planet with beacon, so I get research projects about it and about destroying it, and after that I still have those events, that slows down research.
Actually there are a few more bugs in this save:
1. You may see two of the defeated empires still in the diplomacy screen with 0 planets - worth checking too why they are there. The same with some pirates.
2. After acquiring some abandoned ship (I explored the whole galaxy before that), I received the nav coordinates in the nebula (bottom left part of the map, as far as I remember), but nothing happens - the nebula is fully explored and there's nothing to do, but the coords still flickers on the map.
3. The save is really buggy, it constantly crashes the game. I messed up a little in the game editor (basically created an "ultimate" star system for humans), but I don't think it's related to it. Maybe it's related to the colony policy - I'm exterminating everybody, except humans (don't judge me

)
I know the galaxy is huge, which can explain #3 crashes, but my system is quite good - i7 13700, 128gb RAM, Nvidia 4080, game is on M2 SSD.