The biggest problems with gRPC are:

1. Very complicated. Way more complexity than you want in most cases.
2. Depends on HTTP 2. I've seen people who weren't even doing web stuff reach for gRPC, and now boom you have a web server in your stack for now reason. Compare to Thrift which properly separates out encodings, transports, etc.
3. Doesn't work from the web. There are actually two modifications to gRPC to make it work on the web which means you have three different incompatible versions of gRPC with different feature sets. IIRC some of them require setting up complex proxies, some don't support streaming calls, ugh. Total mess.

Plain HTTP can be type safe. Just publish JSON schema or Typespec files or even use Protobuf.

I mean, REST-ful JSON APIs can be perfectly type-safe, if their developers actually take care to make them that way. And the self-descriptive nature of JSON is arguably a benefit in really large public-facing APIs. But yeah, gRPC forces a certain amount of type-safety and version control, and gRPC with protobuf is SUCH a pleasure to work with.

Give it time, though, it's definitely gaining traction.

It's the recommended approach to replace WCF which was deprecated after .NET framework 4.8. My company is just now getting around to ripping out all their WCF stuff and putting in gRPC. REST interfaces were always a non-starter because of how "heavyweight" they were for our use case (data collection from industrial devices which are themselves data collectors).

I like the concept and I think the use case is almost covered by generating API client through generated OpenAPI spec.

It's needs a bit of setup but a client library can be built whenever a backend server is built.