Hi John H Shaffer,
Welcome to Microsoft Q&A. forum.
The number of devices you can install Microsoft 365 on will depend on your subscription, however all subscriptions allow multiple installations. Generally, most Microsoft 365 plans allow installation of Office applications on five PCs or Macs, five tablets, and five mobile phones, totaling fifteen devices per user.
Understand subscriptions and licenses in Microsoft 365 for business.
Minimum: There is no strict minimum, as even a single device can be covered.
Maximum: The majority of Microsoft 365 plans permit installation on up to five PCs or Macs, five tablets, and five mobile phones, per user. Business plans extend support up to 300 users, meaning a single company could have thousands of devices covered.
Enterprise plans (like E3 and E5) have no cap on users, so organizations can cover thousands of devices depending on their licensing agreement.
If the information is helpful, please accept the answer by clicking the "Upvote" and "Accept Answer" on the post. If you are still facing any issue, please let us know in the comments. We are glad to help you.