You might often find Apex Legends getting stuck at “Party not ready” after hitting the Start button. We have been there too, and the fix that mostly works is restarting the game.
Every time you find Apex Legends stuck at Party not ready for longer than usual, exit the game and relaunch it. If restarting the game doesn’t fix the problem, then perhaps you need to restart your system as well.
If you’re partying with friends, ask them to restart their game and systems as well. If you’re on PC, and “party not ready” doesn’t seem to fix at all, you can try to repair Apex Legends via Origin.