I can confirm that allowing QuickBooks 2023 to install updates (currently at release R3) before opening QuickBooks 2021 (currently at release R12) has fixed this error on multiple computers that previously couldn't edit transactions in an accountant's copy. To see your current release, open QuickBooks (any version) and hit {Control}+{1} to open the Product Information dialog.  You should see the product release you have installed indicated at the very top.

Thank you Susanlynnmiller!