Some more info and I think this thread can be closed: I noticed that when opening other apps, sometimes there is the same blank gray sqare (like "DVE" to view waves of Verilog simulations, on old server running GNOME2 there was icon of it) and sometimes there is an icon ("nedit", "soffice"). It seems to me the problem is ouside the scope of PerlTk program and is somewhere in the EL8+GNOME3 graphical system... Thanks for all the answers.

In reply to Re^4: PerlTk GNOME3 alternate icon file shown as blank square by kaza_perl_ip
in thread PerlTk GNOME3 alternate icon file shown as blank square by kaza_perl_ip

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