Explain / Summarize effects of Tx Tagging disablement on multiple VLANs simultaneously

I am new to Zyxel Switches and at least for me, the "Tx Tagging" option in the VLAN Setup screen seems a bit confusing. On the one hand, seems to only apply to (inbound) traffic that is untagged - on the other hand there is no restriction that disallows disabling it on multiple VLANs for the same port at the same time.

Also, there is no overview screen where I can see (for a given port), what VLANs have this option disabled and no clear guidance on the behavior in such a case, i.e. which VLAN tag is actually added for untagged traffic (potentially depending on other active scenarios such as MAC / Protocol / Subnet based VLAN settings).

A hint / message when disabling TX Tagging on multiple VLANS explaining the expected behavior (ideally considering the currently prioritized tagging scenario for the port in question) would be very much appreciated.