I was surprised by your comment because I only knew about Australia. It’s 21 countries, but not all enforce it:
Argentina, Australia, Belgium, Bolivia, Brazil, Chile, Costa Rica, Ecuador, Egypt, Fiji, Greece, Honduras, Liechtenstein, Luxembourg, Mexico, Nauru, North Korea, Paraguay, Peru, Samoa, Singapore, Thailand, Turkey, Uruguay
https://en.wikipedia.org/wiki/Compulsory_voting
Mexico looks a bit off there with compulsory voting and 52% turnout… but several countries have 90% or more turnout:
Australia, Belgium, Bolivia, Luxembourg, Nauru, North Korea, Samoa, Singapore, Uruguay
(I feel like north korea doesn’t really count though, and Nauru has 12k residents total)