Photos hard crash when exporting slide show

Hi - I made a slideshow (fairly large, ~200 pictures) with a little bit of text, and every time I try to export to a movie file (.mv4 seems to be only option), it starts but stops part way through and the app just quits/disappears, and the ForceQuit window pops up asking if I want to quit other apps. I have hardly any other apps open and plenty of room on the hard drive. (oh, also no sound track on the slideshow)

Thanks for any hints! All images are mine, not from a shared folder.

Just installed BigSur and update, v. 11.0.1, and Photos version is 6.0 (311.0.130).