Windows 10 PRO 20H2 to 21H1 upgrade fails on reboot

I have several computers running W10pro and all except 1 have automatically upgraded to 21H1 (even a 2005 dell core duo laptop)
However my main computer (ASUS MB/8gb ram/6 core AMD processor/lots of free drive space) fails to complete the upgrade. It is currently Version 20H2 10.0.19042 Build 19042.

After completion of the install (30 min process) on final reboot rolls back to 20H2 (about a 10 min process) without any error warning or other message. Log files created only show warnings for "telemetry disabled" and "battery monitor is waiting" (like a desktop has a battery !!!)
I have only windows security running, have administrative privilege's, have run all the appropriate troubleshooters and tried other suggested fixes. The problem remains after 3 attempts to upgrade using upgrade assistant and upgrade via manual upgrade.
Upgrade assistant will run saying OS/CPU/memory and storage space OK. Process will start and then reboot after about 30 mins. That first reboot is OK then more background installation process and second reboot occurs. After the second reboot the log on screen appears for about 5 seconds and then another reboot followed by the message "reinstalling previous version" or something like that. The rollback goes smoothly and everything works OK except I am still on 20H2.
I want to upgrade since things like printer sharing seems not to work when all systems are not on same OS version.
Any thoughts to help me out?

Have you tried using Media Creation tool on your Asus computer to obtain 21H1 and see if that works?
The motherboard has a battery.

The MS troubleshooters found no problems with upgrade process. I only tried the Media Creation tool once and upgrade assistant twice. I will give it another try tomorrow. And will run setupdiag also tomorrow. Security is only Windows 10 security that comes with Windows 10. Fully active and log file generated by failed upgrade attempts does not show any problem due to firewall.

This is a homebuilt PC with ASUS MB/AMD 6core CPU/8GB RAM/AMD Radeon 6570 video card. OS Win10 Pro 32 bit. OS and hardware drivers are as up to date as MS and vendors have available.

Boot drive is 256GB SSD with two partitions one 252MB system reserve partition and the other the main 223GB boot partition that contains programs and OS.

Data/System backups are on larger 1.5TB internal SATA drive.

I would prefer not to do clean reinstall of the OS but if I did would probably choose the 64 bit version since my computer is capable and my license is either 32 or 64 bit.

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OK
Ran Setupdiag. Results highlighted Operation failed: Enable Page File in SafeOS. Error: 0x8007023E[gle=0x000000b7]
occurring right at the end of the installation (last reboot).
Researched that on the internet and lots of possibilities. Most suggested fixes were pretty complicated and did not seem to work for others. Video card driver seemed most likely but I had the latest AMD driver even though it was 2015 was MS certified.
One optional update was for an "alcor USB driver" which I had never installed since everything seemed to be working fine. I updated that driver.
Then I ran across an easy to implement series of steps (that I felt would not corrupt my current install.
These steps were:

1. Go to the Windows search bar and type services.
2. Double-click on the Services app and scroll down to Windows Update.
3. If the service is already running, right-click on it and select Stop. Then restart it.
4. If the service is disabled, right-click on it and select Start.
5. Additionally, make sure the Background Intelligent Transfer Service and Cryptographic Service are running.

I made sure these 3 services were running and then restarted each of them.
Rebooted the computer and ran the Windows 10 update assistant again. This time the update completed successfully and I am now running 21H1. I do not know if it was the USB driver upgrade or the services resets that corrected the problem but each were painless to implement.

And in response to earlier posts yes I do know that the MB as a BIOS battery but that is not what battery monitor checks. Battery monitor is not even on my OS. And I also know that my 32 bit installation can only use 4GB of the RAM on the MB. I have more RAM because I was given some and I will probably upgrade to 64 bit OS in the future.
Thanks to all who made suggestions.

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Upgrade worked but all Chrome bookmarks (about 900) and passwords disappeared. I don't sync with google but probably should. I did have weekly Macrium disk images so I was able to retrieve them. Couldn't find them on Win10 restore points.

Thanks I didn't know that about restore points.

I am kind of a belt and suspenders guy so in addition to the weekly Macrium disk images of the C drive I also clone my C drive once a month so the bookmarks were in both of those places.

Also I like your tag line.