and if IIRC widgets and plasmoids work differently now.

https://develop.kde.org/docs/plasma/widget/porting_kf6/

https://develop.kde.org/docs/plasma/theme/theme-porting-to-plasma6/

Maybe Borg is a possibility. However, I have not yet backed up an entire system with it, but only certain files.

• The file permissions have always been correct when restoring files in my case.
• Which compression (LZ4, zlib, LZMA or zstd) and which compression level is used can be specified when creating a backup.
• Backups can be mounted via FUSE, so that you can restore individual files with an file manager or a terminal emulator, for example.

There is no such thing as the objectively best solution. Each tool has advantages and disadvantages. And every user has different preferences and requirements.

Personally, I am using Borg for years. And I have had to restore data several times, which has worked every time.

In addition to Borg, you can also look at Borgmatic. This wrapper extends the functionality and makes some things easier.

And if you want to use a graphical user interface, you can have a look at Vorta or Pika.