What did you mean by highlighting doesn't work on mobile versions? Did you meant the bold tag or something else?
Highlighting and adding the bold tags work. I was specifically saying you cannot highlight a text and then add the option to change colour. If you try it with other bbcode tags, it will be applied to the highlighted text, but when trying to change colour the tags show up in front of the text and not around it.
You can try it on your mobile device to see how it displays.
But, that's because of the way the browser mobile handles the layout of the site.
Unfortunately, there is not much that can be done. The forum is not responsive. It is not prepared to work perfectly in the mobile browser, so it generates this situation.
In this sense, there is no way to solve it. You just have to change the way you use that feature.
Instead of writing and then adding the BBCode code, you first add the code and then write.
I guess that't understandable given the situation. We are almost at 2026 and yet we are using SMF 1.1.19 (a decade old version, isn't it?). So I'm guessing some things are bound to be un fixable at this point.
As for the feature part, I do the opposite actually! I write it somewhere else (notepad), then edit it, add the desired BbCodes and when I'm finished, I post it here! In this way, I just have to remember each bbCodes and their functions. Yes, not very convenient way of doing it and it consumes more time, but I'm used to it that way!