Linux performance is worse than Windows or FreeBSD on the same hardware

I am using OBS 28.1.2. I previously used 27.2.4, so this is not a new issue. I have tried both on my laptop and my desktop. I've tried using both Ubuntu Studio and Gentoo (I tried using Fedora at one point, but I think I may have had issues where I couldn't enable hardware encoding). Hardware acceleration for video encoding works fine on both Windows and FreeBSD. But despite OBS saying that hardware encoding is enabled, the video encoding performance is identical to software rendering performance when I run under Linux. Clearly it is not an issue with the quality of the open source drivers; otherwise performance on FreeBSD would be expected to be just as bad. I have an AMD video card, but I'm using the integrated graphics on the Intel CPU for the video encoding. Has anyone else had this issue? If so, have you found a fix for it?

For comparison, I get about 32ms to render a frame on Linux and about 2.5ms to render a frame on Windows and FreeBSD, and I drop about 7% of frames under Linux while I get no dropped frames on Windows or FreeBSD. This is rendering at 1280x720 at 30 FPS on my desktop.

I forgot to mention this in the original post, but I have tried running under both Wayland and Xorg. It made no substantial difference.