From 18 months ago I baught my Pc :
Ryzen 9 3950x - 32GB Ram - Gigabyte RTX 3070 TI - MAG B550 Tomahawk MB - MAG 240R Liquid Cooler - 750W Power
After 7 months from using it the temperature become 60 at the Idle mode then 95 from 1 month ago.
MSI replaced the cooler for me with the new version of the cooler 240R V2 and I used Mastergel Maker New Eddition 11W but I found that the temperature now after the new cooler and the new thermal paste is still 85c at the Idle mode
What can I do
Don't know if its your specific cooler, but I do know one of MSI's AIO cooler kept getting a recall because the pump was always breaking. My first suggestion would be to reseat the cooler just incase of poor contact, but I doubt that's the case since you were getting decent temps until a month ago. I'd personally just go with another brand of AIO because I'm thinking your pump has failed or starting to fail.
One of the reasons I'll stick to air cooling.
That's subjective and really up to your personal preference. I know some people who use air and get top of the line cooling like the Noctua DH-15 or 360 AIO's from popular brands like Corsair, Artic, etc. It really depends on your preference. You can't really do wrong with either, but for me, I feel its more fail points in AIO's which is why I choose to use Air coolers personally.