Is there no User Guide / Manual pdf for Catalina ?

I generally find google works best. EG - want to know how to search in macos.

Search for

Macos search.

The first link is the apple support page about spotlight.

Or just go here:

https://support.apple.com/en-gb/guide/mac-help/welcome/10.15/mac

and open the table of contents.

That would come to thousands of pages, are you up for that, and anyway I doubt that exists.

Buy a book macOS Catalina The Missing Manual is always a good start.

Available in bookshops, online and here, https://books.apple.com/us/book/macos-catalina-the-missing-manual/id1490182061

I am thinking of the link you gave or the user manual under the Apple icon-About this Mac-Support

It does not look like thousands of pages - but it would be nice to read it as a pdf because then I can make annoations too, and I can navigate it easier.

Then print it to PDF.

Author David Pogue has been writing his “Missing Manual” series for a very long time. He is well known in the Apple world for his excellent work in helping users learn how to use all things Apple. You might take a look at his missing manual for Catalina. It’s available though Amazon. The Kindle version is only $10.

Catalina Missing Manual