On MacOS, how are brew services different from launchctl services? is there a way to use snap on a Mac to run services instead of brew?
Brew handles the complexity of parsing each package and then issues the appropriate launchctl commands for you. So in the end, launchctl and launchd do the lifting, brew just is an intermediary to make it easier for you to get going.
% brew services -help
Usage: brew services subcommand
Manage background services with macOS' launchctl(1) daemon manager.
If sudo is passed, operate on /Library/LaunchDaemons (started at boot). Otherwise, operate on ~/Library/LaunchAgents (started at login).
This is all covered well in the first 6 lines of the help and you can inspect the code in github if you are curious how this actually works behind the scenes.
I don’t know about snap, so perhaps a follow on question explaining more what you want to do there would be a good next step if needed.