Cannot make game window wider than 4074 pixels

I'm using a 7680x2160 monitor (57" Odyssey Neo G9) and I'm unable to play the game in wide windowed mode. This bug report isn't complaining about the black bars - they are there as expected in fullscreen / windowed fullscreen modes (https://imgur.com/a/48uq9y6). However, in windowed mode (the primary way I play PoE), the game window refuses to resize beyond 4074 pixels wide (https://imgur.com/a/tqIETf0), regardless of the vertical resolution.

To play in 21:9 windowed mode, I'd need the window to be able to resize to 5040x2113.

Same issue with the same monitor. It's very annoying as I see no point in playing in max resolution after GGG removed 32:9 support. I can rather use the space the black bars take for a browser window or whatever, but when using windowed mode it's not possible to use more than 16:9...