Can my friend extend his tourist visa in Chiang Mai for 90 days or only 60 days?

30days extension (once) is the only extension available for tourist entry (entry on SETV or visa-exempt scheme). 60days entry on TR visa can be extended for 90days TOTAL with an extension.

I think there could be some 'lost in translation' or just misunderstanding - total 90days and 90days extension are often mixed up.

But as mentioned above, OP's friend could have a chance to apply for Covid extension on or before 26 Nov, if he have less than 45 days (in CM) in his latest stamp after he applies 30days tourism extension. (But 60days would start on the day of application)

Anyway, I guess he has almost no chance to get 60days or more extensions with his stamp.

He can get 30 days or maybe 60bdays if they let him have the covid extension

What visa did he enter on, and what extension of stay is he attempting to acquire?