Creating a slideshow in Elements 2022

As a rule, I would agree with what Glenn has said about the length of a slideshow.  But there are exceptions to every rule and perhaps your project is one of them.  So, to answer your question, as Glenn has said, the limit for each slidehshow in the Organizer is 250 photos.  But you could always create multiple .mp4 video files from the Organizer's slideshow tool and combine the video files into one long file.  You can even use Windows' Photos app to combine the mp4 files.  (I'm assuming that you intend to play the slideshow via a computer file and that you don't intend to create a DVD playable on a set-top DVD player.)  And as Glenn has also said, if the Organizer's templates don't suit your needs, you should be looking to other software including Premiere Elements which can handle an unlimited number of photos.

You can't "work around" the 250 image limit.  Use Premiere elements for stuff like that.   Why do you want to make such a slide show?