MS Access Database and Windows 11 Update error

[The_Doc_Man]

1. All the databases are "Protected" after I removed their "Read Only" marks (Access can still write into them) but they cannot be synchronised,
meaning I cannot back them up. Perhaps Microsoft want us all on OneDrive (it is a no no as far as I am concerned).

Synchronized? As in "cloud-sync"? You CANNOT run Access on a back-end file hosted via ONE DRIVE, mostly because of protocol issues. The cloud does what it does via whole-file protocols (similar to FTP). Access REQUIRES (and this is an "absolutely requires" case) the use of SMB (Server Message Block) protocols - the standard Windows File and Printer Sharing protocols. Even for cloud files, if no one is IN the database, at least for Access it is true that a manual copy of the whole file (to a non-cloud folder) is a reasonable backup. Maybe not desirable - but workable. That is not always true for separate SQL-engine databases like SQL Server or ORACLE, which CAN defer some tasks to background status as a potential speed hack.

3. I cannot create a local network between the computer (I can reach the laptop by creating a connection using the internal IP address which is router depended (When I change to a router that has Internal IP address (e.g. 168.192.??.??) I will have to change the connection.

Have you tried UNC-based network links? \\computer\drive\path\name... ? Does require that your machine names are available for local name services to find them. Could also indicate that you need to change some of your computers from DHCP (internal automatic IP assignment) to manual fixed-address assignment and then create ROUTE tables to point to the network path through your routers and manually enter some NAME TABLE entries in the hosts file to lead to those named systems. Because from what you describe, you don't have a domain-based network, just an in-house network.

4. Notwithstanding, one database somehow manged to get onto the laptop but it cannot be opened by Windows 10. IOW Windows 11 IS NOT DOWNWARD COMPATIBLE!!!

I have not seen that - but there IS still the question that relates to Windows and Office libraries. Once a particular Access app has been run on a higher-level version of Office, the library links are automagically updated. After that, you cannot go back to the lower level of Office - but that isn't a Windows issue. That is due strictly to the Office libraries. THOSE are not downwards compatible.

Windows (by itself) is only a file-share facilitator for Access files. There is no such thing as a change of code from Win10 to Win11 that affects the way files are copied (in the absence of cloud contention). All Windows CAN do at that level is to assure a valid and true copy has been made.

Sorry, have no comments on your points #2 (keypad) and #5 (repeated failing login).