Somewhere between 6.0 and 7.0.10 the treatment of special value "ZBX_NOTSUPPORTED" has changed. Previously it was possible to make an item "unsupported" by returning "ZBX_NOTSUPPORTED" in a custom script run by zabbix_agent2. Since 7.0.x this value is treated like any other regular data, which may lead to incidents such as misbehaving LLD scripts spawning lots of invalid items and triggers (a case which was always avoided by letting Zabbix know that it must not expect data in case of script errors).

Steps to reproduce:

1. Create a new Item with Type=Zabbix agent, Key=mytest;
2. Define a new custom script in Zabbix agent 2 and restart it: UserParameter=mytest,/path/to/script.py
3. In /path/to/script.py write to stdout like so:
   import sys
   sys.stdout.buffer.write(b"ZBX_NOTSUPPORTED\0My error message")

Result:
Item receives literal string value of "ZBX_NOTSUPPORTED" as if it was a normal value.
When testing for value the item has a normal value of literal string "ZBX_NOTSUPPORTED".
Expected:
Item turns "unsupported" and an error message is displayed next to it in Latest Data.
When testing for value the item is marked as "Not supported" and there is a non-empty error message.