You can believe it.  Virtually all professional tax products are Windows-based, AFAIK (except, of course, those that are cloud-based).

If your client doesn't want to dual boot (and I don't think you can anyway if your client has the latest ARM-based Mac computers), your client could consider installing Windows as a guest within MacOS using VirtualBox.  The other alternative is to try Wine but it may not run properly or at all.

Otherwise, your only option is to revert to the trusted proforma PDF organizer or the less ideal (in my personal opinion anyway) Questionnaire/Documents Checklist in Intuit Link.