Exactly. People with English as a second language go from meaning to writing. Native speakers go from sound to writing.

There, their, they’re is something native speakers confuse as well. I have only ever observed native speaker write should of instead of should‘ve or should have.

Pretty much only native speakers have problems with this

99% agree with this. This is a native speaker issue, except where someone took up bad habits from the natives...

Pretty much only native speakers have problems with this

That makes no sense since they would use it more, however native speakers from the US do have problems with it, and other words (they're/their).

Rarely encounter it with others.
Their spelling is embarrassing, same as their very limited vocabulary. IDK what they do in schools.

Maybe, yes, but as someone who has seen tons of unedited writings, I can tell you those mixup as common as muck.