Running LO 126.96.36.199 on Ubuntu 16.04 LTS. Trying to print an envelope to a Canon MG-6320. Print is being directed to the upper paper/cassette tray. I cannot find any way to direct it to the lower tray where the envelopes are loaded. Don’t say “just load the envelopes in the upper tray”. They don’t fit there - it is sized for smaller photo paper or CD/DVDs. There is no problem with normal documents going to the correct tray - just envelopes.
Do not say “just load the envelopes in the upper tray”.
I can only say that it is not a problem of LibreOffice. Look in the manual of your printer. Search there for the description of which paper tray is intended for envelopes.
Envelopes will not physically fit in the upper tray.It is specifically sized for CD’s or their labels. So there can only be one tray “intended” for envelopes. Also, doing the same operation from MS Word on my wife’s laptop, to the same printer, causes no issues at all.