TT4 Custom: locking-symbol on the far left side: do you have any idea!?

i am currently starting to customize the theme twenty-twenty-four – (tt4): i have to say i love it.
its an awesome new theme with a fresh design.

while customizing i found out that there is a “locked” symbol in the template customization. See the image well i do not know what does this mean!?

does this mean – that the template or the tempalte part is locked!?

see the image: https://imgur.com/a/wQdDzE6

look forward to hear from you
regard