Is it possible to connect to a Microsoft Access (.accdb) database in ArcGIS Pro?

Yes, it is possible to connect to a Microsoft Access (.accdb) database in ArcGIS Pro. This capability is introduced in ArcGIS Pro version 2.6.

Microsoft Access databases can be read in ArcGIS Pro using the OLE DB database connection. Refer to ArcGIS Pro: Create an OLE DB connection for instructions to make an OLE DB connection in ArcGIS Pro.

Note:
On the Provider tab, select Microsoft Office 12.0 Access Database Engine OLE DB Provider. The Microsoft Office 12.0 Access Database Engine Provider was installed with either Microsoft Office or the Access Database Engine. See the help document Work with OLE DB connections.