So in this scenario I'd need to double-up all fields of this type?
Are custom field types still a 'thing'? Is there any documentation around how to create these? I couldn't see anything obvious.
I've noticed that for editing, Query Tag uses select lists rather than autocomplete and the lookups for these could include up to 8000 items, which presents a problem as these are all loaded into the DOM.
A previous version of the site I'm working on (created by a separate, now retired developer) used custom field types. This was back in the days of Joomla 1.5.