Typing pinyin tones on iPad with an external keyboard (iPadOS 14.3)

There seems to be no way to type pinyin tones on an iPad using the "Chinese, Simplified - Pinyin" keyboard when using an external keyboard (Magic Keyboard in this case). In MacOS I can do this by typing the syllable and then tabbing through the tones (tap once for mā, twice for má etc.) and with the on-screen touch keyboard on iOS or iPadOS I can hold down the key until the tones appear and then press the one I want; but when using an external keyboard neither tab nor holding down a key works.

A previous topic gave ABC Extended keyboard as an option, but this does not appear in my list of available keyboards; perhaps it got lost in the update to iPadOS 14.

I can still input tones by reaching over to the iPad and bringing up the on-screen keyboard, but the whole point of having an external keyboard is so as not to have to do that.

Probably only learners of Chinese will be bothered for this, but I'm learning Chinese and I'm very bothered by this, so I'm asking here.