First I cloned the physics2d repository from the unity github account. When I played the editor it started instantly. But I created a new empty project in the same unity version. I pressed the play button from the editor again, but this time it was delayed.
Unity Version : Unity 2021.3.5f1
That’s because the physics2d repo has enabled a setting that disables domain reload when clicking play mode. Go to Edit > Project Settings > Editor, enable Enter Play Mode Options and then disable Reload Domain. You can also disable Reload Scene, but it usually doesn’t make a huge difference.
Using these options requires some special care with some stuff, like static and private variables, specially if both options are disabled. There’s more info in the manual and in the forum. You can also give me a shout if you get stuck with something related to this; I’ve acquired a good amount of experience dealing with problems related to these settings.