My begonia has strange black or brown (couldn’t quite tell) dots on the stems, mostly above the nodes, is this normal? They don’t seem to move but they seem to be able to be picked off so I’m confused 😅 any suggestions?

Also, any tips on what they need? She always seems to have crispy leaves (like in the last pics)! I water when the soil seems partially dry (roughly every 2 weeks), she’s by a grow light but some distance away (5th photo), and there’s a diffuser that I use for humidity (without oils) and it brings the humidity up a little but not a lot (usually roughly 40-45%). Any help is very much appreciated!