In some versions of M365 and Access 2021 under Windows 11, Combo Boxes with the Auto Expand property set to "Yes" do not expand correctly to match the values typed in them. Some reports of this behavior indicate it to be inconsistent, but that it recurs in databases where the problem has appeared.
In two cases, the version of M365 used by the reporting person was specific to Educators, although two others reported with this behavior did not identify an Educator version specifically. See, for example, these discussions:
Several Access Builds have been reported to exhibit this behavior, including:
Microsoft® Access® para Microsoft 365 MSO (versión 2310 compilación 16.0.16924.20054) de 64 bits
Microsoft Access 2021 MSO (Version 2310 Build 16.0.16924.20054) 32-bit
Microsoft Access for Microsoft 365 MSO (Version 2309 Build 16.0.16827.20166) 32-bit
Cause
The common denominator for this problem appears to be in newer builds of Windows 11 rather than any change in Office, as suggested by the different builds of Access.
Workaround
Dropping the list in a combo box alleviates the problem.
Status
A fix for this issue has been delivered in update Version 2312, January 4, 2024. See the Version History Page here.
NOTE: we also confirmed that having ANSI 92 Compatibility turned on in an accdb causes this problem. If update version 2312 doesn't correct the auto expand problem in your accdb(s), check whether you have ANSI 92 Compatibility turned on in them. If you need ANSI 92 Compatibility, you need to wait for Microsoft to deliver a fix for this configuration.