It is not an Archicad setting but a Windows setting.
Control Panel > Region and Language > Formats > Advanced Settings > Digit Grouping Symbol.
If you do change it you may find that existing dimensions will not change - only new dimensions you place.
Also if you share the file with other users on other machines you will need to make the same change there.
I don't particularly like the comma but have grown used to it and I don't bother changing it as we are constantly swapping machines in our office.
Barry.
One of the forum moderators.
Versions 6.5 to 27
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11