I like to keep much text information collected in the schematic (things like requirements etc) but sometimes it can be nice to not want to show everything.
Is there a way to place text on another layer which I can turn on and off as I want before export etc?
Changing your habits is probably a much better option.
I also tend to make some small lists and/or tables in a KiCad schematic. A table for jumper settings is for example a good use.
However, as soon as documentation gets more elaborate, it is much better to move such documentation to a separate text document in the project directory.
You can also embed datasheet links to schematic symbols, and those datasheet links do not have to be .pdf files. KiCad just gives the link to your OS to figure out. It can also be a word processor file, html formatted stuff or whatever. It is quite easy to make a schematic symbol as a placeholder for link to your own documentation. That means that your documentation is just a single button press away from within your schematic. And because they are separate programs, you can scroll pan and zoom though them independently, and that is a productivity boost too. Having a big monitor and/or dual monitor setup is really handy with KiCad.
Those files also show up in the KiCad project manager, and it has a button for opening the project directory in a file browser. So there are plenty of opportunities to get to your documentation quickly.
Having layers in the schematic may be a useful thing, although I never missed them.
Another simple possibility is to put those texts outside of the schematic paper boundary. I use the area around the paper extensively for temporarily parking all kinds of snippets. It’s a multi layer clipboard with visual feedback for me.
A dangerous option if someone writes something that they shouldn’t. Even worse if a PDF plot faithfully hides it in the output.
If you just want notes, why not create an extra sheet?