This problem is caused by a broken configuration of BOINC in the Ubuntu 22.04 (Jammy) repository, a search will find many forum posts discussing the problem.

My tested fix is to issue these four commands from a terminal window.
Edit2 - especially for beginners, the changes from the usermod command will not take effect until you log out and back in or better still reboot the system.

sudo systemctl enable boinc-client
sudo usermod -a -G boinc $USER
sudo chmod 664 /etc/boinc-client/gui_rpc_auth.cfg
sudo systemctl restart boinc-client

reboot the computer and login.
Start BOINC Manager, if it runs all is well so register for your project.

From this post... Edit - user should be $USER, the user name you are using on linux.
https://boinc.berkeley.edu/dev/forum_thread.php?id=14792&postid=110892

The error is corrected in the reply post.

Occam,

Please note this:

sudo usermod -a -G boinc user

has been changed into:

sudo usermod -a -G boinc $USER

So, try this again, as Country Bumkin suggested:

sudo systemctl enable boinc-client
sudo usermod -a -G boinc $USER
sudo chmod 664 /etc/boinc-client/gui_rpc_auth.cfg
sudo systemctl restart boinc-client

Adri

For 22.04 I installed an older version from the 20.04 repository. I had to hunt for them but used a 20.04 install to get the package numbers.
There were 6 files. I marked them not to be upgraded.
boinc
boinc-client
boinc-manager
libboinc-app-dev
libboinc-app7
libboinc7

First I had to uninstall the files mentioned above.

To make the install work I had to add or upgrade other files eg: libjpeg62-turbo libssl1.1
All the libraries above including the libjpeg and libssl had to be installed in the one "sudo dpkg -i <list of packages>" command so that they could satisfy all the dependencies.

After installing the libraries I installed the three boinc files listed above.

This might not everything - looking at my bash history it looks like I uninstalled the boinc-manager again, maybe I only remotely manage this device.

uninstalling (repeated this for each of the files listed)
sudo apt-get remove libboinc-app-dev

Installing the libraries (after downloading them) (I didn't type the file names in - I typed part of them and used tab expansion to complete the rest of each name)
sudo dpkg -i libboinc-app-dev_7.16.16+dfsg-1_amd64.deb libboinc-app7_7.16.16+dfsg-1_amd64.deb libboinc7_7.16.16+dfsg-1_amd64.deb libssl1.1_1.1.1n-0+deb11u3_amd64.deb libjpeg62-turbo_2.0.6-4_amd64.deb

Installing the boinc application (after downloading them)
sudo dpkg -i boinc_7.16.16+dfsg-1_all.deb boinc-client_7.16.16+dfsg-1_amd64.deb boinc-manager_7.16.16+dfsg-1_amd64.deb

setting up boinc to run
sudo systemctl enable boinc-client
sudo systemctl start boinc-client
sudo chmod g+r /var/lib/boinc-client/gui_rpc_auth.cfg
sudo usermod -a -G boinc $USER

telling apt-get not up upgrade these files in the future
sudo apt-mark hold libboinc-app-dev libboinc-app7 libboinc7 libssl1.1 libjpeg62-turbo
sudo apt-mark hold boinc boinc-client boinc-manager

There are probably other things i did to get it working (sudo apt-get update etc etc)

One note: In the future, linux users will have to use a PPA for the latest boinc-client code. BOINC is moving away from individual maintainers and will be maintained exclusively by David Anderson's team.

See: https://github.com/BOINC/boinc/discussions/5315