Edit: After further testing, it appears Start11v1 (1.55) doesn't like the updated Widget. Turning off the Widget makes it work like usual.
But if you wish to keep using the Widget, temporarily disable it, go into Start11's taskbar page, make the changes you want, set taskbar enhancement to off and then re-enable Widget. Some of Start11's configuration are still on (mostly colors and transparency do work, but not features such as Start11's ungroupping of taskbar icons. Windows 11 own version will take over)
I updated to the latest version (from unknown version to 1.55, I updated sometimes early summer the last time) on saturday to get the Widget back, since Microsoft changed things again. Just installing the update did not make it return, but turning off and on the "Let Start11 enhance the Taskbar" feature, as well as restarting Explorer made it work.
This worked for half a day, but when I stood up this morning (no reboot inbetween), the configure button as well as most things on the right side of the taskbar (widget and system tray) acted strangely. I've rebooted once, but that didn't help.
It takes about 5-10 seconds for the hidden icon box to appear (if it appears).
Clicking on "Configure Start11" makes the menu stick and nothing happens for about 30 seconds or a program "resets" the taskbar, making me having to click Configure Start11 again.
When either of these happen, the open/stickied part of the taskbar doesn't work either. As long as I don't try clicking on the system tray or configure, I have no problems clicking on the program icons/names.
The Start part seems to work regardless of if the taskbar is locked up or not.
This issues appear to disappear when I turn off the Enhance Taskbar feature of Start11, which is one of the main/only reason I still use Start11