I am wondering how I might check, if WSL version 2 is running? Where and with which command, it might get the version of WSL?

wsl -l -v

Under Titel: BOINC Client installation in WSL and link to a project, there is a Note: “WSL, by default uses all available cores and memory of you PC”and a command

notepad "$ env: USERPROFILE / .wslconfig"

When I execute this command, I get the following error (Spanish): “Bloc de Notas, El nombre de archive, el nombre de directorio o la sintaxis de la etiqueta del volume no son correctos.”

I would like to ask: where, with which name and with which extension the file shall be saved?

That will be revised shortly, and should have said
Open the Windows command prompt and type:
cd C:\Program Files\BOINC and then launch the following command from that directory:
boinccmd --gui_rpc_port 2536
(this is one random example, put whatever you want). This will set the Windows BOINC port to 2536, while the WSL port will remain 31416.

The agenda for Community Discussion + Tutorials on April 28 has not been posted yet but World Community Grid Tech Keith Uplinger has an exciting announcement for that day:
"I am planning on doing a tutorial similar to what I did in Chicago about setting up a BOINC server and running from scratch. My plan is to have it run on ubuntu 20.04 for ease of use for those to set it up."

I was just wondering if the BOINC add-on webpage was going to be updated

Projects which have closed down usually - eventually - make that visible publicly. Either they post a polite notice of thanks on their website, or their domain registration lapses and gets taken over by a spammer.

If you come across one of those, it's worth posting the information to the mailing list Jord mentioned. But a message board thread is an inefficient tool in those circumstances - the people you most want to be aware of and act on the information, are the least likely to read it here.

I'm not sure when the projects list is updated, but its accuracy depends on input from the science projects. BOINC itself has no control over them rather providing an advertising hoarding for projects that are using the BOINC environment.
The BOINC project itslef does none of the computing, provides no server space, administration staff, science staff etc. to the science projects.

If the closed projects don't tell that they have closed (there is a projects email list they can email that to), nor the new projects say that they are new and in production, it's no wonder the developers don't know about these things. New projects that are still in alpha/beta stage will generally not be added to the projects list.

That notwithstanding, the following projects listed in the BOINC projects-listing are essentially defunct:

Asteroids
BOINC@Tacc
CSG
Cosmology
...
ETC.
I'm not going to waste additional time of mine finding viable projects. The fact is that a significant number of BOINC projects - 2/3's ??? are not viable - in that there is NO activity on the respective BOINC-community message-boards.
You BOINC-people look into that, I'll look into this, and we'll see where the twain shall meet.

But please, reintroduce the button for download boinc client.

But, if i'm not wrong, i remember that SU receives funds from NSA....

I think that was presented as NSF, but you may be right.

MLC@Home is down.

I would expect to find a big download BOINC button on the BOINC front page, just as it used to be. Go to any other website which is for its own (named, brand) product, will you find when you get there that it advertises a completely different thing with a small link to the actual product? No. So why that need here?

Apparently BOINC has been killed.