TCA: readOnly renders as 'disabled' element instead of 'readonly'. 'passthrough' type renders nothing (not even a hidden field). No way to pass default IRRE child 'type' values.
Please read here:
It would have been a good idea to continue at that old ticket, since the issue is still the same. But I guess nobody is reading that ticket, because it had already been marked as rejected and probably won't show up in the usual "list all fresh unresolved tickets" dashboards.
Now there's apparently a regression - so please check out https://forge.typo3.org/issues/32412#note-6 and re-open that ticket (or continue here).