For the handful of other Linux users out there, I finally got the game to run at reasonable performance.
I'm running on fairly low-end hardware with laptop's integrated GPU, so if it works for me, it should be enough for anyone. Also I'm running on Ubuntu 20.04.
I installed Lutris and added the game executable into the game list, default settings (DXVK, VKD3D and Esync on) and wineGE 6.21-1.
After attempting to run the game, the menu screen was black and Lutris prompted me to install wine-gecko. The process was automated, just hit "install".
The menu screen was black for maybe half a minute longer, then everything seems to run about as well as you could expect.
Interacting with characters sometimes gives an up to 10 seconds delay, but it's not so common as to make it unplayable.
Framerate I had around 20-30, but I have all my CPU cores at full use, so it's probably not an issue in wine.
I have not played through the whole game, but so far nothing game breaking except occasional crashes.
What I have tried previously and did not work:
Wine on 32-bit prefix + gecko.
Wine on 64-bit prefix + gecko. (Runs at about 1 FPS)
Proton through steam (Add non-steam game).
PlayOnLinux with default settings. (Might have worked but I couldn't install gecko due to checksum mismatch)
Windows VM. (Runs at about 1 FPS)