What is recommended to do with older Versions of Elements when we get a new Version?

@gfmucci 

You asked:

Is the old version's Catalog and all its settings totally imported into the new, 2021 version?

Remember that the organizer is coming from the integration of a separate organizer tool twenty years ago.

The first versions were built on a Microsoft Access database engine until version6 replaced it with a more powerful one, Sqlite (also used by Lightroom and numerous other apps).

The principle is that you can 'convert' older version catalogs into the current one. Obviously, some features have been superseded by new ones, like the slideshows, but the catalog structure itself well preserved. There is even a process to convert the old Access ones used before PSE6.

What happens to all the settings in the Organizer of the older Version when the new Organizer is installed?

You have to redefine all your preferences.

Is the old version's Catalog and all its settings totally imported into the new, 2021 version?

I keep old versions installed, however I don't use the Organizer at all.

There are some features not available on newer versions.

It's a matter of personal preference.  Some folk keep older versions of Elements because they prefer the slideshow feature.  There are a couple of other features that have been removed over the years.

The programs are entirely independent and I do not believe that any preferences are carried over from one version to the other.  (In some cases, I wish they did.)