Most usually the software that is available in the repositories is the latest version guaranteed to work with the current system. A lot of the times though you can get out of your way to compile from source and that would still work, but again no guarantees.
I just tried myself with the latest version of Timeshift and while it did install, the UI doesn't launch at all so the only option left is the command line. I tried timeshift --create and it stood there without doing anything for a while. Unfortunately I'm not familiar with the Timeshift, so I don't know if I should provide some additional argument or maybe is just doesn't work.
You can also try with a different version and see if you have better luck with that, instead. But ultimately, if you don't actually need the latest version possible there's no reason to worry about it.
It's probably due to some missing dependency version or it simply hasn't been tested and included in the repositories yet. In their website they also list an option to install through PyPi for the latest version, so it's worth a try:
Yes, but those apps are updated. I know because I switched back to Ubuntu and when I install them via sudo apt install solaar, timeshift last version is there.
Why that is not the case on Zorin as it is also Ubuntu based
It appears then, that these are the versions offered as stable in the Mantic repo. If you need a later version due to certain bugfixes or additional features, you can use Flatpaks.
This is an odd one. Timeshift works properly in previous versions. Have you tried troubleshooting the apps in question?
Sometimes, when having trouble with an app, it being too new can be an issue as much as being too old. I often will roll back to a previous stable version before trying a newer (and potentially buggy since all the new bugs have not yet been worked out) version.
You are comparing the Mantic Mintotaur repos with Ubuntu 23.10, to Zorin OS (16.3 or 17 Beta?)
You are wanting the latest versions of Solaar and Timeshift on Zorin OS, not Ubuntu 23?
The packages you referenced are available on the Interim release distro of Mantic Minotaur, not on the Stable Release Jammy Jellyfish repositories that Zorin OS 17 uses.
I notice that the github of Timeshift also does not show a version 23:
Has this changed maintainer?
You could test the Linux Mint version:
Solaar is available on Github with the release version you are looking for: