I have the same issue as Socrates. I couldn't tag him, quote him or reply to his post without additional lines being entered. Even typing this freeform was having the issue, I ended up having to log in on my PC to finish this post.
Using desktop mode on my mobile browser (Brave) still had the issue of adding new rows.
I don't know if maybe it is some sort of Android keyboard compatibility issue with the forum software, but it bites. I know my mobile recently updated to Android 13, and I didn't notice having this issue until after that point.
The more you try removing the auto-inserted new rows on mobile, the faster and faster they add in. The most I've been able to manage without having the new rows issue is typing a short sentence without quoting, replying, tagging, inserting any elements, or pasting any text into the draft.
I've had this issue as well in the past, before my mobile keyboard stopped working on the forum. I ended up converting .webp files to .mov to get around it.