There are legitimate reasons for someone on the right to mention Soros, such as his funding of “Media Matters”.
Here is a list of projects funded by Soros, all progressive leaning
That is the legitimate context of mentioning his name, that and any other thing he funds. As you have mentioned, Koch is the alternative on the Repubiican end, or at least they were.
I can’t help with what far right groups might alleged because I don’t go to anything like that, or at least nothing further right or extreme than Breitbart.
Of recent the commonest way I have seen his name mentioned is by someone or group from the left claiming that whenever “Soro’s” name is mentioned, it really means “the Jews”. Which I consider nonsense and divisive to the extreme. When I hear Soro’s name mentioned in a funding type situation, it usually means “Soros”. And it is mentioned of recently not nearly as much by the right (or at least by the not extreme right) as it is by the left.