actually, major distributions esp. from the Debian and aff. branch (Ubuntu, Mint, Devuan, Deepin, etc.) change divers definitions creating maximal disturb on the PC's of owners of non free hard and firmware (I use DELL PC's with Intel stuff in then since before year 2000!).

if you actualize your Linux actually, you are probably not able any more after that.

is there a way to make only a partial update of the installation so that it doesn't touch at all the kernel, initrd etc.?

how to do to reinstall OLD KERNELS (older as those of the actual level of the distribution) with all old settings?

How are you updating your packages? You should be able to select only the packages you wish to update. There should be a confirmation before you update anything you don't want to update.

For older packages, have a look at https://snapshot.debian.org/

If you are using Ubuntu you can use Synaptic package manager, find the package you want to keep from updating, highlight it, on the left side pick Package and highlight Lock Version and lock it, that package won't update any longer, make sure you lock all the packages that require that package for updates, for example the kernel you want to lock the linux kernel package, the kernel headers package and the kernel image package so that when you run update, it won't come up to update. This can be used for any installed package, I don't remember if it worked in Debian the same way.