Hi, can I use 20W fast charger adapter for charging my Iphone Xr every day? Is it even safe?

It will not harm battery life, but it also won’t charge the Xr as fast as it would charge an iPhone 11 or iPhone 12. It is a “smart” charger; when you plug it in the phone tells the charger what voltage to provide and the charger adjusts its output to what the phone has “requested”. It will only use 12 watts of the 20 watts that the charger is capable of providing.

yes, you can use a 20W charger, it's safe