What make/model PSU?
You could try running the program called DDU to remove all past/present drivers .. reboot . .and THEN install latest GPU drivers from AMD.com website
Make sure you have the latest AM4 chipset drivers installed from AMD.com website as well
Good practice to run separate power cables from your power supply to each power input on your GPU
I treat my motherboard BIOS's like drivers and always keep mine up to date. (X470D4U, B550m Phantom Gaming 4, B650E PG Riptide, B650E Steel Legend)
Maybe run
sfc /scannow
in a command prompt as admin to check for and hopefully fix any corrupted system files
Maybe run an offline scan with Windows Defender just to make sure you are not infected with anything
Have you recently installed any software that might correlate with your recent issue?
I ran a similar monitor config with my 6700xt with a Samsung 1440p 27" 144hz, 4ms primary and an ASUS 27" 1080p 60hz and now currently with a 7900XT with no lag type issues
Prior to that I ran a 24" ASUS 1080p 144hz, 1ms primary and an Acer 24" 1080p 60hz on my old 5700xt .. never experienced laggyness on the 60hz monitor