Hello Dan, this is Emily.
If you go to Settings > Apps > Apps & featues, you would see "choose wehre to get apps", please pick "anywhere'.
If you don't see this option at all, then it is likely you are on S mode. You can type winver in the search on the taskbar and hit enter, it will pop up a small window and see if it mentions S mode. In that case, you need to switch out of S mode in order to have this option (to download outside of store app). I attach the instruction in case you need it: https://support.microsoft.com/en-us/windows/swi...