How to disable this unicode auto completion?

Hello,
I wanted to type the German word “Niedrig” but the result is “N𝑒𝕣𝑔”.
I have completely disabled auto correction on input.
What is this?

Video:
https://www.youtube.com/watch?v=amb7FRjoS_M

I can’t reproduce the described behavior. Most probably, there is something in your setup. Read these guidelines and ask a good question.

Looks more like a problem with the system’s input method editor / keyboard mapping / modifiers / … that replaces a sequence of two characters, specifically

ie => “𝑒” U+1D452 MATHEMATICAL ITALIC SMALL E

dr => “𝕣” U+1D563 MATHEMATICAL DOUBLE-STRUCK SMALL R

ig => “𝑔” U+1D454 MATHEMATICAL ITALIC SMALL G

Take a look at menu View, if Input Method Status is not greyed out try what it does.

Found out it’s in other programs too. So it must be a system setting.