I just found this patch and it seems to work fine. It even upscales the videos. Its from 2021. Give it a try:

zombs-lair.com/post/definitive-edition-patcher-septerra-core

I downloaded this patch and everything LOOKS great, but I am still having a few issues.

1 - the mouse still seems to be a bit choppy, even moreso when moving the mouse while moving the character around. Using a controller somewhat allivetae this as the mouse speed when using the controller stick is much slower (I don't like using the controll because it doesn't seem optimal and movement feels jerky).

2 - I am a streamer planning to stream this game, but I need to be able to alt-tab to do chat commands, but when I alt-tab, the game loses track of my mouse and won't go back into the game. Is there a way to fix this?