A new SCROOMAGE Demo update has been released that should address majority of the severe performance issues that can be seen on lower-end hardware! My apologies for being radio-silent for so long, this has been a pretty big challenge that required a significant re-factor of majority of the game's active code.
If you haven't received the update automatically from Steam, you can right click the game in your library, go to Properties, and click "Verify the integrity of the game files". For anyone whose curious about the changes, below will contain a rough list of all of the differences I've made.
Optimizations
The game's object spawning system has been fully re-worked to be a queue-based distribution system, which distributes the load of processing items during playtime
All of the most common game objects additionally are cached at level load-time with several copies, and objects are re-used instead of being deleted at their finishing point. This means that for the most part, the game does very little loading of assets from the disk after the level loads, in most cases. This change is what has helped the performance the most on lower-end hardware. This will result in higher memory usage, but the trade-off is very much worth it.
The entire codebase has been sifted through and cleaned up to cache as many node references in the scripts as possible, reducing unneccesary CPU usage
Enemies when close together will now share one navigation agent in a leader-follower type of setup, which reduces the amount of navmesh pathing that has to be done
A custom occluding scheme was created to replace Godot's occluding system, allowing for maps to be sectioned out instead of being mostly rendered all at once on every single frame
The physics framerate has been cut in half to 45fps (versus 90 before) and many items are interpolated more than they were before
Gameplay Changes
Enemies can now jump and get up over slopes. This may lead to strange cases where enemies get stuck in some geometry, but it's worth how much better their movement is right now.
A new gun has been added, The Micro-SMG, which is a weaker version of the P60 bullpup gun. It is intended to act as a bridge between the weaker pistols and the larger automatic guns
The starting pistol has been nerfed, with the firing rate being reduced significantly and damage slightly nerfed. My reasoning behind this is that I found in a lot of cases the pistol to be a strong enough weapon to contend at nearly all times, albeit less efficiently than other guns, which ends up clashing with some of the level design to escalate fights over the course of the entire map.
And that about settles that! You may see some more unintended behaviour given the nature of how large of a shakeup this has been, but the game's performance should generally be much better on most hardware at this point. Have fun!