Is there ever a good reason to change from monolith to microservices unless you have already solved the factoring problem in the monolith? The factoring problem doesn't get easier because you add network calls into the mix, but being well factored first makes adding the network calls a lot easier. If you're lucky your framework or platform already has that part figured out.
Maybe one exception is if you absolutely must change the programming language at the same time, but even then I would suggest doing the rewrite as a monolith first for the same reason, so you again don't have to deal with network calls at the same time as solving an already insanely hard problem.
There's the argument that microservices lets you gradually replace the old monolith piece by piece, but there's nothing special about microservices for that, you can do that with two monoliths and a reverse proxy.
And at the end of either you might find that you didn't need microservices in the first place, you just needed to factor the application better.
Maybe one exception is if you absolutely must change the programming language at the same time, but even then I would suggest doing the rewrite as a monolith first for the same reason, so you again don't have to deal with network calls at the same time as solving an already insanely hard problem.
There's the argument that microservices lets you gradually replace the old monolith piece by piece, but there's nothing special about microservices for that, you can do that with two monoliths and a reverse proxy.
And at the end of either you might find that you didn't need microservices in the first place, you just needed to factor the application better.