PCB manufacturers specify their minimum via sizes. Probably that is the smallest usable drill bit size made in quantities. JLCPCB says minimum 0.2mm so there's

PCB manufacturers specify their minimum via sizes. Probably that is the smallest usable drill bit size made in quantities. JLCPCB says minimum 0.2mm so there's what you got. Keep in mind you will need a air bearing spindle that runs at high x10k RPMs to actually use them. For smaller holes we zap them in the material with lasers.