I have a BrandX 27.5 diameter 85mm dropper post, which could do with pressurising. The top of the cartridge is not a Schrader valve, but appears to be a 5mm female thread, into which would screw an adapter.

It looks like a shock valve adapter tool might do it. Do you know the thread size on a Monarch tool like this? Alternatively, there is a Marzocchi one which looks similar. Monarchadapter

Decathlon shock pump comes with an adapter. https://www.decathlon.co.uk/p/fork-shock-absorber-pump/_/R-p-436

I had a lapierre branded dropper that used the above adapter but it would just let air out when unscrewing the adapter.

Thanks for that, I’ll check out the Decathlon one.