When my friend was getting his stuff out of his tamed donkey with a saddle on it (sneaked and right clicked the donkey), I jumped on his donkey. I went into my/ the donkey's inventory, and he crashed. This was on a vanilla server. No, he did not give me the crash report. To do this bug again, do the same thing we did.
Please attach the complete output of the "Development console" of the launcher. CTRL-A, CTRL-C there, CTRL-V in the ticket.
If the launcher closes after game start, please edit your profile and select at "Launcher visibility" "Hide launcher and reopen" or "Keep the launcher open"