Mainly because I installed it and ran it on a sample base infra - vpc and subnets - and I noted that it was still picking up Hashicorp providers, fine, but doesn’t this mean I have to run through a large codebase and start switching every provider out? Essentially I wasn’t sure what to do next. Should I stick with my standard terraform setup or figure out shifting to OpenTF and risk getting hit with something not available? Wasn’t something I could figure out in advance, if that makes sense? So was safest to stick with TF.
You should just keep using hashicorp providers - there's no changes to your codebase required, generally, as long as you don't specify provider sources in long form (as in, you should specify the source as `hashicorp/aws`, not as `registry.terraform.io/hashicorp/aws`). All providers should be available in our registry, and if you're missing any, just submit it[0]. Though as I said, all should be available.
There's also the migration guide you could take a look at[1].