You will have to update to Windows 11 at least October next year when Microsoft support ends for Windows 10 and there are probably no security updates any more. It's similar to the Windows 7 > Windows 10 update. The sooner you do it, the less it will hurt.
However, in your case you seem to have some kind of image postprocessing in your video driver active or as app. Some games have a gamma correction setting for real fullscreen mode that influence brightness, may be such a setting is also present in your graphics driver or with whatever extra app you might use for augmenting video output.
OBS itself doesn't do this. If this was general OBS behavior, the forum would be full of reports similar to yours.
found someone with a similar issue
they have a similiar graphics card to mine (7800 xt vs 7900 xt). It probably has to do with the graphics driver indeed.
I tried recording with Adrenaline and that works as it's supposed and image looks normal. I wonder what kind of recording it does because it does neither the DXGI raised gamma issue i'm running into or the yellow border thing.
I could try to DDU the driver and do a clean install of the driver. Will update if I get around to it.
For now i just used the Color Correction filter in OBS and used a -1.05 value which brings it close enough to what i need it for as a temporary patch. Not perfect though i can either go lower and the get crushed blacks or too high and get overexposed whites.
offtopic: as for the win11 thing, considering the resistance to upgrading to win11 they might extend support for win10, like they did for xp. or they might iron hand it to force everyone to upgrade but i dont know if they have the PR for that with the ad and AI bs they've been trying to push.
