Since about 2 weeks ago I can't play any games smoothly in fullscreen/borderless anymore as long as my secondary monitor is connected. The frametimes are the same as with only one monitor connected but the gameplay feels very choppy and not smooth as it would when I play the game in a window. The stutters stop immediately when pulling out the HDMI cable of the secondary monitor. I can't remember that I changed anything that caused this problem to just randomly start. Strangely sometimes when I cold boot my PC the issue is gone only to appear again the next day.
Things I tried that didn't change anything:
DDU Radeon Software and only installing the AMD drivers (Chipset and/or Graphics)
Closing any other program besides the game itself
Disabling any startup apps
Disabling/enabling Adaptive Sync/Enhanced Sync within the Radeon Software
Disabling/enabling Variable Refresh Rate in Windows' settings
Try a different secondary monitor
Checking Windows for corruption (DISM/SFC)
GPU: RX 6650XT
CPU: Ryzen 5 3600
Main Display: Acer XF240H (144Hz, 1080p, Free-Sync, connected via DP)
Secondary Display: Benq RL2455 (60Hz, 1080p, no Free-Sync, connected via HDMI)
I'm out of ideas other than buying a team green card. Thanks in advance for any help.