[Patrick C]

Provided I didn’t mess up, the following should do

^[Α-ΩA-Z].*$

Where
^ start of string (i.e. line)
followed by a character within [Α-ΩA-Z]
followed by any character (except newlines) .
occurring zero or more times *
$ end of string (i.e. line)

Let me know if it does or doesn’t work.

Cheers

Patrick

PS The full syntax would be
/^[Α-ΩA-Z].*$/gm