I installed the latest version of BOINC (7.24.1) for Windows on my Win 11 system. Prior to the installation I had pinned the BOINC Manager app to the taskbar so that I could easily access my projects' status. Clicking on the taskbar icon would display the Manager screen. After the installation I deleted the old pin and pinned a new copy of the BOINC Manager app to the taskbar. When I click on it now nothing happens.

I can still bring up the display using the BOINC task tray app.

Why has the taskbar app behavior changed?

Have you tried deleting the shortcut to the app on the task bar and creating another one? My other question for those who have used Windows more recently than I have is whether this could be related to whether BOINC is installed as a service or not?

Are you sure you picked the BOINC Manager app from the programs listed in the BOINC directory? There are several there, all with the same icon.
boinc.exe is the client (no GUI).
boinccmd.exe is the command line/terminal command app (no GUI).
boincmgr.exe is the BOINC Manager app, the only one with a GUI.

However, if BOINC Manager is already running, as in available in the System Tray, you cannot start it again by clicking the BOINC icon in the Taskbar. You then have to open BOINC using the icon in the System Tray.

Yes I picked the BOINC Manager app from the BOINC directory. I would like BOINC to start on login and be able to display the Manager from the taskbar. I don't recall having an instance of the BOINC Manager in the system tray before the latest install.

I think the full answer to the problems with the system tray icon and the Manager full display will depend on your version of Windows, and the precise 6-monthly patch upgrade that has been applied to it.

Under Windows 7, the system tray icon is displayed, and double-clicking on it restores the running copy of the Manager to display in the foreground - with v7.24.1, as well as all previous versions.

But starting with Windows 10, Microsoft wants us to start referring to this bit of the screen as the "notification area", and the way they manage it seems to change every six months. To start with, there was a very clear and accessible configuration window which allowed you to choose between "Only show notifications" (default), or "Show icon and notifications" (the old way). But over the years, that configuration page has been doing a fine impression of the Cheshire Cat - vanishing slowly, a bit at a time, and becoming harder and harder to find. Because there are so many variations, it's hard to give good generic advice, but many suggesteions have been posted in internet fora and help pages. If you give us your full Windows version number and patch level, somebody could try and dig one of them out for you.