Hello Bill, thanks for your commitment
Some feedback first:
- The suggestion from Jord did not have any effect
- Neither did it work stepping back to version 7.16; I'm again on the latest "stable" release: 7.20.4

Answering your own questions:
1. On a M1 Mac - as far as I understand - there's no difference between CPU/GPU, right?
2. Where should I look for "Leave non-GPU tasks in memory while suspended" ? (Sorry... I didn't find this option)
3. While BOINC Manager is active, mouse moving does not cause any progress resetting. (Anyway, progress was kept for 2 of the tasks on 0.000% until it reached 1%.)
BUT those two tasks DID reset their progress display while resuming activity after having been suspended through computer activity!

Thanks for further help, if possible

Here's a copy of my event log.
Any help will be appreciated.

It is a shame that the AMD drivers are such a mess among the various generations of AMD cards. They do have the performance there . . . if you can get past the installation of working drivers.

You are running the service version of BOINC. The BOINC client runs in the boinc group and belongs to that group as well as the video group if you use the gpu.
Your user needs to belong to those groups also.

You will also need to add yourself to the boinc group in order for the Manager to connect:

# usermod -a -G boinc $(whoami)

You can check the users in the boinc group with:

$ groups boinc
boinc : boinc video

Check your file permissions of the gui_rpc_auth.cfg file. It should have a 640 or 755 attribute. There should already be a softlink to the file in the /etc/boinc-client directory.
Make another softlink to the file in your home directory.

$ cd ~/
$ ln -s /var/lib/boinc/gui_rpc_auth.cfg gui_rpc_auth.cfg
# chmod 640 gui_rpc_auth.cfg

You can either null out the default hashed password or put in your own. Save the file and reboot and you should connect the Manager to the client.

No, not that way. app_config.xml doesn't pass enough information back to the server about what work you can handle..

As a matter of interest, why wouldn’t max_concurrent = 0 work?

Hmm. Hadn't thought of that :-)

My worry would be that BOINC downloads a task, but never runs it. Bill would be fetching tasks from Einstein as normal, with no control over what comes down the line - rather different from, say, 'resource share 0' for a backup project.

One of us should try it sometime ...

If the command lspci shows the intel GPU, then it might still work.
it's an older architecture, but not all Intel IGPs are supported.

There are only a few projects supporting Intel CPUs.
You'll need to install OpenCL for Intel

See this post:
https://boinc.berkeley.edu/forum_thread.php?id=13256&postid=96195

00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)

Does intel_gpu_top work? (Install Intel GPU tools)

(intel_gpu_top:12236) intel-mmio-CRITICAL: Test assertion failure function intel_mmio_use_pci_bar, file ../../lib/intel_mmio.c:145:
(intel_gpu_top:12236) intel-mmio-CRITICAL: Failed assertion: !(error != 0)
(intel_gpu_top:12236) intel-mmio-CRITICAL: Last errno: 13, Permission denied
(intel_gpu_top:12236) intel-mmio-CRITICAL: Couldn't map MMIO region
Stack trace:
  #0 [_init+0x7b87]
  #1 [_init+0x5420]
  #2 [_init+0xe85]
  #3 [__libc_start_main+0xe7]
  #4 [_init+0x1c92]
Test (null) failed.
**** DEBUG ****
(intel_gpu_top:12236) intel-chipset-DEBUG: Test requirement passed: pci_dev
(intel_gpu_top:12236) intel-mmio-CRITICAL: Test assertion failure function intel_mmio_use_pci_bar, file ../../lib/intel_mmio.c:145:
(intel_gpu_top:12236) intel-mmio-CRITICAL: Failed assertion: !(error != 0)
(intel_gpu_top:12236) intel-mmio-CRITICAL: Last errno: 13, Permission denied
(intel_gpu_top:12236) intel-mmio-CRITICAL: Couldn't map MMIO region
(intel_gpu_top:12236) igt-core-INFO: Stack trace:
(intel_gpu_top:12236) igt-core-INFO:   #0 [_init+0x7b87]
(intel_gpu_top:12236) igt-core-INFO:   #1 [_init+0x5420]
(intel_gpu_top:12236) igt-core-INFO:   #2 [_init+0xe85]
(intel_gpu_top:12236) igt-core-INFO:   #3 [__libc_start_main+0xe7]
(intel_gpu_top:12236) igt-core-INFO:   #4 [_init+0x1c92]
****  END  ****
FAIL (-1.000s)

According to Intel's website:

To allow NEO access to GPU device make sure user has permissions to files /dev/dri/renderD*.

sudo add-apt-repository ppa:intel-opencl/intel-opencl
sudo apt update
sudo apt install intel-opencl-icd