There’s actually a workaround for this on mobile, which would be to use an Airtable automation instead.
However, you wouldn’t be able to use a button field anymore, because for some odd reason, Airtable has decided that buttons and automations are 2 separate things, and that buttons can’t trigger automations. Makes no sense.
So, instead of using a button, you’d have to use a checkbox field instead. Whenever you check the checkbox, the automation would decrease the number by 1. And you can even make your automation clear out the checkbox after you check it, so it’s ready to go again for checking again.