/proc/sys/fs/inotify/max_user_watches is the current max number of watches per user.
Historically, the kernel has defaulted this to 8192, but given that many Linux distros customize their kernel builds quite a bit, this may not be true on every Linux system. A recent kernel change [1] dynamically selects a default max_user_watches value in the range [8192, 1048576] based on how much RAM the system has. (5.11 is the first kernel release containing this change.)
AFAICT, root can change max_user_watches to any value that’s 2147483647 (231-1) or under, as long as you’re confident you have enough RAM to support that number of watches.