But till GTK 4 arrives there is no possibility to move these buttons ?
Not as far as I can tell.
How you gonna do if the infobar will be deprecated ?
Well, its the least of the issues for GTK4, its only deprecated, it __shouldn't__ be removed until GTK5, the problem is the widgets that are deprecated in GTK3 and removed in GTK4 and other non-backward compatible changes in GTK4. But that will take a GTK expert to contribute fixes to both Geany and Scintilla.