In Quick Mask mode, you can paint with brush and leveling tools selections. That's great and simple. With the key "Q" to activate this mode (selected areas are displayed by default as red) and with a second keystroke you leave it (the selected areas are now displayed as the typical ants lines again.
Quick Mask mode accidentally activated
Sometimes, however, one gets randomly on the button "Q", activates the mode and suddenly many Photoshop features stop working as usual, they are grayed out in the menu, filters are not available and so on. Although you can see at a glance in the Layers palette that the mode is active, because the active layer appears highlighted in red in the Layers palette, in this case, and the corresponding button will appear pressed in the toolbar, but you know how the in the heat of the moment is so.
The masking mode is also saved!
So it was a reader who always had the problem with a single file that certain features simply were not available and "the planes blocked" were recently. For the Tückische that the condition of the masking mode when saving a TIFF, PSD or PSB file is also stored.
So if something should not work as expected again, check first of all, whether the masking mode is turned on accidentally. 😉
Best regards and have a nice weekend!