Just a small FYI post here, as I wasted a bit of time figuring this out recently.
My profiling tool of choice is Pix For Windows, which I've been using for years on UE4 projects. Hooking it up was simply a matter of enabled the console variable
This has not been working in UE5, since Early Access, and didn't work in 5.0 release either. Anyways, I had a poke through the engine code and realized Epic had refactored the way external profilers are handled. You now need to add the following command line option, to use Pix.
I hope this saves some people a bit of head-scratching!