A family of Microsoft relational database management systems designed for ease of use.
Teams is not an option for shared accdbs, nor would OneDrive and other similar locations.
There are probably other ways to get the current tables to migrate, but there is an initial limitation that may be what is impacting you here.
Instead of trying to upload 20,000 records in a table in one go, try creating temp tables based on your other tables. Limit them to fewer than 5,000 records in any one table; that's the critical limit for indexing. Once that's done, additional records can be added.
Once the smaller recordsets have been used to create the original migration, you can append the remaining records from each table.
Try that first with one table as a test. If it goes okay, you can complete the task with the remaining records and other tables.