Can uninstalling the LTS version of a program and installing the latest version cause any system problems?
Seahorse is on version 43 while LTS remains on version 41 and I don't know which security patches have been applied.
Steam, Lutris, etc.
Another example is Telegram, which is included in the system store as a Zorin OS package but has been out of date for at least a year and could lead lay users to install it by mistake instead of the Flatpak version.
What is the best way to get the version of these and other applications when using Zorin OS, apart from the Flatpak version?
I mean to install their non-LTS versions without conflicting with the available LTS versions.
Is there any chance of a non-LTS version of Zorin OS based on Ubuntu, or a way of transforming the system into the non-LTS version without losing the benefits of this operating system?
There usually is no danger of uninstalling software from your computer, so long it's not listed as a dependency from other system components. This can be sometimes tricky; for example, in Zorin OS certain fonts are dependencies of components from the desktop environment, and uninstalling them could cause breakage. You can check this by running:
apt show seahorse
Which would show you information about the package, including required dependencies. Or attempt to remove it with:
sudo apt remove seahorse
sudo apt remove seahorse
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following packages will be REMOVED:
seahorse
0 upgraded, 0 newly installed, 1 to remove and 1 not upgraded.
After this operation, 2,417 kB disk space will be freed.
Do you want to continue? [Y/n] n
Abort.
This would list all the programs that are going to be removed, or are no longer required. In this case only the seahorse package will be removed so it should be safe to do so. Notice at the bottom that you are asked if you want to continue with the operation, in case you are not sure about it.
This would be a good time to mention that taking snapshots of your system using something like Timeshift may save you from accidentally deleting something you didn't intend to.
It appears that Seahorse is now only maintained as a flatpak although, oddly enough, its supposed to be only at version 42. You can see the change log here.
You shouldn't install two versions of the same software, use one or the other; you can however have a native .deb package and a flatpak version, if you want to.
Most of the time you will find that Flatpak has newer versions of software as it's designed to allow developers a faster release cycle. In contrast, distributions like Zorin OS inherit the release cycle from the Ubuntu base it is based on, where software is tested at specific versions to ensure the best reliability with the rest of the system. This does not necessarily mean these packages are "outdated"; I would suggest you use these first unless you have a reason to use the a newer release.
I highly doubt this will come from Zorin OS. It's just not the intention of distribution. If you need to use the most up to date versions of software, you should look into a rolling release distribution, OpenSUSE Tumbleweed, Fedora, Endeavour OS, etc.
Something I've noticed is people tend to think they need the latest possible versions of software. But latest doesn't always mean better. Everyone's use case is different, of course, and only you can decide whether you really need to upgrade to the latest possible version. I thought I mention it as it's something that comes up often.
If you want to have the most up-to-date Software Version and You won't use Flatpak (or Snap) You could go to the Developer's Website from the Program and download there directly the Linux-Version of the Program.