this is what i do everytime and it works on my pc:
Xbox Game Bar
Xbox Game Bar is pre-installed in Win 10 and 11. It's able to record up to 1080p resolution at 60 FPS.
Note: To avoid black screens during the recording process, you need to turn off the feature of "Hardware acceleration" first.
● Chrome: Settings > System > Use graphics acceleration when available > Disable it.
● Edge: Settings > System and performance > Use graphics acceleration when available > Disable it.
Step 2. Press Windows + G to open the Xbox Game Bar.
Step 3. Play the OnlyFans video.
Step 4. Press Win + Alt + R to start recording. Then press Win + Alt + R again to stop recording.
I never tried it for fanfix but it works everytime for onlyfans