You’re confusing “microservices” with dependencies on a particular platform (presumably cloud providers). Microservices aren’t more likely to have these dependencies, as monoliths are often also deployed on cloud providers and assume a particular database, etc.

Anyway, if you’re dealing with microservices “lock-in” isn’t a real problem—you just move one service over to your new platform at a time. Good luck doing that with your monolith without decomposing it into services (and frankly, if you can feasibly decompose your monolith into services, your architecture is probably cleaner than 95% of monoliths out there).