magento2.3.5 p1 – Template hints checkbox grayed/greyed out in ALL scopes

For unknown reasons I am currently unable to modify the setting for enabling template hints, although this was possible at some time in the last month, as evidenced by the fact that the default hint keyword “magento” was changed to “hints” by me.

Store is in developer mode. In all scopes – default, Main Website, or Default store view – the checkboxes in the Debug section of the developer panel are grayed/greyed out:

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I have tried cleaning the cache, removing /var/view_preprocessed, & removing the /generated/code folder.