Latest version of the game lags like hell for me in all animated scenes after the first few. I thought it was due to the increase from 1080p to 1440p and then to 4k for some of the videos, that or the mixed video formats. I was worried I would need to re-encode all the videos myself, but it turns out that all the lag is due to a bug in Renpy.
This has now been corrected so I've attached the fix here for anyone to just drop into their game folder. (For any skeptics, this is just the latest files directly from the github page, I just cut everything else out to lower the download size, feel free to check yourself for those with unlimited bandwidth though)
You still need a computer than can handle the videos, so if that's why you lag then this wont fix it, but if like me you have a computer that can handle the videos just fine outside of the game, but lag like crazy when played within the game. Then this fixes that issue, so far as I have tested anyway.
Just download whichever version you need, windows or Linux, extract to the root folder and click replace when prompted.
Hopefully this will be included by default in the next game update, whenever that may be.