Allen screw blocking cassette tool
 

I don’t know if I’ve been out of the game so long that I’m forgetting stuff, or if this is new to me, but I can’t get the cassette tool in there with that set screw sticking out. There’s another set screw on the other side of the axle, but loosening it doesn’t seem to let anything come out.
https://cimg3.ibsrv.net/gimg/bikefor...8a4521e27.jpeg
How do I remove the cassette?

You could tap one of the lock ring notches with a flat head screwdriver or similar. I agree, something doesn't seem right.

setscrew/
 

try thin nose pliers/forceps to turn the screw in.

Winner! Thank you Bike Forums.
https://cimg5.ibsrv.net/gimg/bikefor...886684c5f.jpeg

Also note that shimano freewheel tools like the one you’re using are actually slightly different from their cassette tool. A proper cassette tool might fit past the screw more easily and will generally get better purchase on the lockring

Pretty sure I have the other one too, but the only difference was how deep it goes, which is why I never cared which one I grabbed. I’ll have to dig it out and check.

If you were able to advance that set screw farther in, then presumably it was not pinching the axle to prevent movement of whatever it was supposed to immobilize. Kind of a bummer that it backed out enough to foul the space for the cassette tool. I’m curious about what that set screw does. On Campagnolo hubs the DS locknut uses a set screw but it has wrench flats, too.

Consider using loktite on the set screw to better secure it in place before reassembly, just a bit
not slathered. Presume the set screw is for a hub with sealed bearings?

Use the proper cassette tool. If you ever have to use Gorilla torque to get the lockring off the freewheel tool can strip or mangle the notches.

Yes, I'm quite sure there are sealed bearings under there (just bought the bike and don't care to check anything that doesn't need service or repair right now).