The issue can be reduced to the form pages of one specific plugin. In the console there appear a bunch of javascript errors. A plugin maintainer had a look into it, but could not find an issue related to his plugin. It is not a pressing issue as now I know what the help would have shown; but since I can't delete this thread, I might as well add the new info to it... ;)
General help
Help Icons - no popover / no help
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