Why can't I put on the breathing apparatus (gta5 ps4)?

I have breathing apparatus but I can't put it on, why?

Can't you put them on from the menu (what was it called again?)?

I've already tried the quick menu, do you have to set something to put it on?

Are you sure you can even put them on outside of the robbery?

Yes you can actually

https://gta.fandom.com/de/wiki/Atemger%C3%A4t#:~:text=Das%20Atemger%C3%A4t%20kann%20im%20Inventar,ausgesetzt%20werden.

Google search: Put on GTA breathing apparatus.

I know how to put them on, but my breathing apparatus is not displayed

That is not evident from your question.

I have breathing apparatus but I can't put it on, why?

Do you have the helmet displayed?