If I try to set pad clearnce to <1mm in Pad Properties > Clearance Overrides > Pad clearance, nothing changes.
If I set it >1mm, the clearance increases.
How do you set the size to <1mm?
What are the board setup clearance settings? Both at the “global” board level and for the net class?
Global = 1mm
Net class = 0.8mm
Can the Global clerance no be overriden?
I believe that is correct, the Board Setup Constraints set the absolute minimum for clearances and cannot be overridden (per the docs). You should set those values based on a conversation with your manufacturer (or just trust the advertised capabilities from the website).