This is common in SMF software as stated by Bitcoingirl.club.
The core editor remains basic, with Ctrl+Z typically only undoing text input, not UI-driven actions like inserting smileys or BBCode tags.
Was the undo (CTRL+Z) option disabled on purpose?
No, It's the default of the forum software.
Or can our script guy (PowerGlove) make some patch
Yes he can but I don't believe is worth the work(could be wrong) .
An extension would be better in my opinion