Have you by any chance hooked the monitor up to another computer? How about hooking a different monitor up to your computer? If it's possible this is the quickest way to find out for sure what's wrong!
It sounds like the monitor is on its way out. Is this monitor an LCD or a CRT? If its a CRT it would make a good boat anchor (usually not fixable). If it's an LCD it can be fixed but it may cost more to fix it than a new monitor would cost.
Asus Zenbook Q508UG-212.R7TBL 2-in-1 Laptop
AMD Ryzen 7 5700U Processor
8gb DDR4 RAM (Soldered on Motherboard)
1gb Western Digital Blue NVMe SSD
NVIDA MX450 (DDR6)
15.6" 1920 x 1080 (Full HD) Touchscreen
Intel(R) Dual Band Wireless - AC 7260
USB 1 x 2.0 - USB 1 x 3.0 - USB-C 1 x 3.1
Micro SD Card Reader
Lighted Keyboard
Webcam/Microphone
Windows 11 Professional
MS Office 365 Family
Logitech Anywhere MX Mouse