I'm also experiencing flickering on Linux. Just started the snow level and was looking for a way to fix that. Tried downloading the windows build and importing it into steam to run with proton, but the flickering seems even worse :(. I'm on an Intel Ice Lake i7 based PC.
Viewing post in Hypnagogia 無限の夢 Boundless Dreams comments
After switching to the Windows version of the game running in Proton the flickering was gone on all of the levels on my Steam Deck. The Steam Deck has custom AMD hardware which means it uses Ryzen. If you are using integrated graphics then maybe your Intel drivers aren’t fully compatible with the game or Proton libraries?