Could try to put those lines step by step in your user.cfg (revert afterwards):
1.
window.mousegrabinfullscreen = "false"
2.
borderless.fullscreen = "false"
3.
hidpi = "true"
@GufraMirtol
Could you try to add the following line to your user.cfg (it lies here: /Users/{YOUR USERNAME}/Library/Application\ Support/0ad/config/):
borderless.fullscreen = "false"
It depends on a platform so generally we just provide options to control quality.
About the first screenshots you could do the following:
Disable Post-processing
Disable Shadows
Disable Unit silhouettes
Disable Particles
Set Model quality to Low
Move the Shader rffects slider to the left
Disable Water effects
Set Texture quality to Low
Set Texture anisotropic filter to 1x
Also you could try to test different combinations of OpenGL/Vulkan (Renderer backend) + GPU skinning on/off
Do you have multiple sound outputs (headphones, speakers)? Could you try to unplug the current one before starting the game and plug again after it started?
OpenGL might not work because of some X11/Wayland bug, outdated drivers or security reasons, like AppArmor: https://gitea.wildfiregames.com/0ad/0ad/issues/7582.
To help us you try to run any other game under OpenGL (like supertuxkart).