It states warn, not error.
Deprecated means its support will be dropped in future versions of NodeBB, but is working for now.
So it's no error you need to fix right away.
And since both are @julian s plugins you can be pretty sure it'll get updated before support-drop
hmm it worked
I installed 3.4.1 but it would not start again, so I changed the line back from 3.4.1 to 3.4.0 and it works now
No errors in log and the composer works now in Firefox
thanks for your help @PitaJ