Restart loop after Ubuntu install on USB

[tea for one]

I did read the original post - there is no need to be irritated by my question.
Recovery mode allows you to repair broken packages and reach a working desktop (assuming your PC is not unduly compromised)

I'll leave you in peace now.

[oldfred]

Windows only installs in old BIOS mode to MBR(msdos) partitioned drives.
So Windows install was BIOS. You then boot from MBR. And boot flag must be on the NTFS partition with boot files. It would not be an ESP - efi system partition.
If you can change boot flags on Windows back to boot & as mfstdata, then I would expect Windows to boot if system is set to boot in old BIOS mode.
Some systems require user to change UEFI/BIOS settings to correct mode UEFI or BIOS, some auto switch based on boot in UEFI/BIOS one time boot menu.

Microsoft required vendors to install in UEFI boot mode to gpt partitioned drives in 2012 with release of Windows 8.
So any system that can support Ubuntu which would have to be newer than 10 years old, is UEFI based.
Did you install Windows yourself in old BIOS/MBR configuration?
Or is system so old that BIOS/MBR was original install, upgraded to Windows 10. If so a lighter weight flavor of Ubuntu will work much better.