Asus (and other vendors) did announce early this year about BIOS updates that add support for 32GB memory modules: https://www.asus.com/News/sM0xuUsZdoY7mp1zNo you can't. That's why they list the capacity.
Asus (and other vendors) did announce early this year about BIOS updates that add support for 32GB memory modules: https://www.asus.com/News/sM0xuUsZdoY7mp1z
The current spec sheet says "max 128GB": https://www.asus.com/Motherboards/TUF-Z390-PLUS-GAMING/specifications/
Therefore, there should exists a BIOS update for that board.