akorn says:
T... I think PbP is one of the safer places to start GMing ...
PbP comes with its own set of challenges. Not least of which is that games are designed with the assumption of sitting round a table (or a VTT, these days) and the GM needs to know the system well enough to make adjustments.
If you have a group of friends who you can play with, I highly recommend that as a way to learn to GM. People you know and trust, who are willing to support you are the best. Absent that, PbP might be easier than realtime strangers-on-the-internet, as, as you say, there is more time to think and plan.
Feel free to reach out for help --not only with GMing-- if you need. You are also welcome to join the (rather quiet at this time)
PbtA GM's Round Table, for GMing stuff or practice.