Questions from.a new one

Generally, the logon just uses the chip UID, and read via a HF and/or LF reader. Such as a KBR1

So in this use case, the UID IS your password, or at least part of it.
You could use only the UID or you could prefix and/or annex it with another word or phrase etc.
You could get a dual frequency reader and use a couple of implants, or 2in1 like an xMagic or NExT.

I’m making it sound more complicated than it actually is.

Where as the text data, URL’s etc You write onto the chip yourself via NDEF using something like NFC Tools

The Computer via KBR1 does not “see” the NDEF, and likewise, the phone reading it, does not see publicly publish your UID, It will launch ( or provide options ) the appropriate app to deal with the NDEF data.
i.e. if it is a YouTube link, it will launch YouTube , but won’t show the UID of the chip *

* Unless the person reading your implant, has and opens an app such as TagInfo etc. THEN tries to read it