I recommend you turn on the auto syndication option on the desktop PAGE if your phone isn't allowing it, you need to link your YT account in Rumble if you want your videos to be posted in your YT channel.
I did that actually. didn't have app initially. tried on my phone and iPad. I even log into YT before I choose to syndicate and it still prompts me to log in... but only through Google which it says it can't do. frustrating. arggg