A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear James,
Good day!!
I understand your concern and to my knowledge, the requirement you are looking for can be achieved by the dependent drop-down list but it can’t be possible via out of the box way in the SharePoint Online. However, you can achieve your requirement via integrating the List with the Power Apps.
So, I suggest you to post your concern in the Power Apps Community - Power Platform Community (microsoft.com) to get the detailed help from the experts.
Apologies for redirecting you to different community as the members in the category posted focus on the users with the Microsoft 365 concern and out of the box concerns on SharePoint Online, and have limited knowledge on the customization of Power Apps, to get the fast and better assistance, we have redirected you in the correct path.
Appreciate your patience and understanding. Have a great day!!
Best Regards,
Sophia