I didn't use Fulcrum with a block explorer so I can't confirm that. But it should work.
After giving up WSL (including electrs and BTC RPC Explorer) I no longer reinstalled a block explorer. I am no longer that much active and I also had much less transactions (hence less to check). So what I'll tell are just theories:

* there's a good chance may not be able to connect as long as Bitcoin Core and Fulcrum are not fully synced; I'd expect you get data only after you see the lines I wrote about in the topic start post

* tcp://localhost:50001 looks good to me, I also use 127.0.0.1:50001:t for my electrum when I connect to Fulcrum


* I did use BTC RPC Explorer with Electrs (see this) for quite a lot of time, but sadly last time I've tried something from my steps no longer worked and I gave up. But I think that since then the Electrs doc is more complete and I've avoided Docker for personal reasons and that may be the easy way.

* I recommend Bitcoin core's blocks\index, chainstate, indexes\txindex and Fulcrum's data folder to be on SSD, else it'll be slow