Unfortunately I’m on my steam deck and have no way to send you a video, but I used the cemetery key, crossed the bridge, fought an archer, then got stuck in the gate and died by fire somehow.
When I respawned in Sacrament I ran back to unfortunately find the cemetery door shut and locked again, and the corresponding key gone.
Idk if the key respawns, but this is unfortunate and has me dreading starting my third new character due to being locked out of content over a glitch.