There should not be any problem writing special CE characters on mac inside ArchiCAD. I am not 100% sure for Lithuanian, but here in Slovenia and also in Croatia everything works just fine. Be sure to have right unicode keyboard layout. Here is an example of slovenian letters (AC11 and leopard) in project info, navigator,... I just checked, and it works in AC10 too. I am not a mac expert, but on my MBP it just works.
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Gorazd Rajh
From AC 6.5 onward, Ryzen 9 5900HS, 48 GB RAM, RTX 3080, Win 11