I have just put a new box together and noticed that when I select suspend under activity it does not actually suspend the tasks, the CPU and GPU are still pegged according to the system monitor.
I have tried both versions of the manager in the repository, (7.18.1 and 7.22.1) the manager did allow me to add projects however and change the computing preferences.

Also if I pause the manager, wait a few mins and resume, I notice the completion percentages don't jump for the work units despite the CPU and GPU being pegged.

OS is Linux Mint 21.3

It is quite a long time since I have used the versions of BOINC from the repository. Just checked that with 7.25.0 suspending via the activity menu immediately changes tasks to suspended in the manager and they stop progressing. If I check with top in a terminal that confirms nothing is using a core at 100%. Most of the time I don't run GPU tasks so can't check that right now.

How do I install versions outside of the repository?

How do I install versions outside of the repository?

Download the source code from Git-Hub
install the dependencies.

here is a link to the packages I needed to install to get ./config and ./make to run. You may have to do a little detective work to find exactly what you need to install with a different distribution. After extracting the downloaded zip, in the directory run

./_autosetup

./config --disable-server

make  

and

sudo make install.

Not something I am comfortable doing, unfortunately.
This has worked fine for me in the past in a VM, just not on this standalone box, interestingly the CPU workload does drop slightly when I suspend it.
(Running - suspended - running again)

Which project(s) is/are you running? This report is consistent with a badly-implemented science application failing to respond in a timely fashion to a 'suspend' message from BOINC.

BOINC itself hardly uses the CPU, and certainly not the GPU. It's the science applications which do all the heavy lifting.