It's not just you: Elden Ring Nightreign's matchmaking is taking forever if it works at all, and there doesn't seem to be a fix—aside from queueing with a full group
First reported by Eurogamer, FromSoftware has acknowledged long matchmaking times for Elden Ring Nightreign despite having 2 million players and counting. The studio's initial suggested fixes are not particularly helpful, especially on PC, and the best solution right now is really just queueing with a full team of three.
In an initial tweet about matchmaking, FromSoft suggested restarting the matchmaking process if it's taking too long—I and the commenters on Twitter thread can tell you right now, that hasn't helped.