Hello, Nitya Deva.
The files in the directory
are helper files, needed by the Linux Mint software management system.
They are not a list of files to uninstall. They can hardly be used to compile a list of software packages, which can be safely uninstalled.
The files do not tell you, whether the corresponding software packages have been newly installed or whether the corresponding software packages have been upgraded instead.
If your Synaptic history really stops 3 months ago, then the most likely reason is that you have re-configured Synaptic not to preserve the history.
Please, let us know the most recent modification dates of the 2 files term.log and history.log:
ls -l /var/log/apt/*.log
Another file which can be used to compile the list of
+ newly added (installed) software packages
+ upgraded software packages
+ removed software packages
is the file /var/log/dpkg.log. Though extracting the needed package names and version strings from dpkg.log is more hassle than simply picking them up from the Synaptic history.
But it would be feasible.
I do wonder a bit whether a pure belly feeling like
Now my system is not as fast anymore as I think it should be.
is a sufficient reason to take any drastic steps like reverting a large number of upgraded packages to their previous versions.