Hello

Has anyone encountered the fact that even though the manager is set to use 50% CPU, it does not work?

I have it set to use 50% of the CPU in my case 10 cores and for a maximum of 50% of the time and since I switched from Win10 to Win11 it uses only 4 cores even if there are 10 projects in the manager..... It has happened to someone ?

OK, you have ten tasks running from Rosetta, so the "use 50% of the cores" part of your configuration is working correctly.
No on to the "use the CPU 50% of the time". The tasks won't start at exactly the same time, and so the number of tasks running at any exact moment will not always be zero or ten, it depends on the exact sample time. Also the 50% of time may not have the same time-base for all tasks, to clarify this - some tasks may have a very short time to measure the 50% of, while others may have a very long time to measure their 50% of.
So all is running correctly.

One thing to consider is that using the "use the CPU for 50% of the time" can induce a lot of thermal stress on the CPU as it is continuously warming up then cooling down, and not in a uniform manner across all the cores.

One thing to consider is that using the "use the CPU for 50% of the time" can induce a lot of thermal stress on the CPU as it is continuously warming up then cooling down, and not in a uniform manner across all the cores.

I never use the restriction on % of time and only use restrictions on number of CPUs to keep the temperatures down. Last summer I did this even with liquid cooling but that is rare because with CPDN and latest types of work the limit is the amount of data my slow connection can manage.

Ok, but the main thing for me is that when it goes under Windows 10, 10 CPUs work on 10 tasks, that is, 1 CPU for 1 task.

In Windows 11, as you can see, 10 tasks are running, but only 4 CPUs

BOINC "assumes" that each task will occupy one CPU core, but Windows 11 task manager aggregates the tasks to give a very distorted view of use, so 10 tasks each occupying one core would show as 5 "complete" cores in use, so give you 5 graphs, but a task rarely actually uses 100% of a core, so the total for ten tasks will always be less than that, especially when using the "% of time" control. This is not shown on the graphs so it is far better to use the tables which show exactly what each task is using in terms of CPU and memory.
In Windows task manager you need to look at the tab that gives the % of the CPU cores that each task is using - noting that, confusingly, these are give in percent of the total CPU, so 5% is one CPU core in use by that task.

Picking up on what Dave said - I totally agree, indeed by using the % of time you may actually be adding to your confusion. For PCs this variable is, today, all but useless, but may be of use to those that want to use phones & tablets as they operate in a very different manner.

OK
So I set it to use 50% CPU and 100% time, but I don't know if anything has changed

Looks like boinc tries to run all workunits on intel efficiency cores.
intel i7-12700k has 4 efficiency cores.