How can I find out whether my homeserver is correctly set up to support sliding sync?

I've used matrix-docker-ansible-deploy to set up Dendrite and the Sliding Sync proxy. Is there a way for me to test the sliding sync functionality?

Try to login with element X?

It requires it, and wont let you set it up if it's not provided by the homeserver.

Element X works, but does it really require Sliding Sync?

Yes. I tried logging into my homeserver from it once, it straight up will not let you continue setup if sliding sync isn't available.

Yes, the entire point is that it is the client where Sliding-Sync is being developed and tested.

Open https://yourserver.example/.well-known/matrix/client and see if this part exists in it:

"org.matrix.msc3575.proxy": {
    "url": "https://slidingsync.lab.matrix.org"
}

if so, chances are it'll just work.

Not really, it simply indicates that it delegates the traffic to the sliding sync proxy. It does not indicate whether this proxy works correctly.

Yeah but logically speaking that's what EX looks fort, and chances are that it'll work (because why else would it be in the response?)