Joe will start the game. How long he lasts and how effective he will be is debatable. I can see him trying to run away from Donald. I think he's been told if Aaron breaks through just go down and protect himself and the ball. I think under any kind of pressure he will intentionally fold up to protect himself.
With Burrow in then the Bengals will be relying on quick short passes, to move the chains. If the Bengals start Browning, the Rams will be facing a guy that has never played in a regular season game. That said he played well in pre-season.
I think the best option for the Browns would be to start Browning and see how he plays. Use Joe as their emergency option. In college Browning was streaky in that he was great for most of the game then he would do something dumb and end up turning the ball over. But when he was on point he was actually pretty good. So IMO it comes down to how much they trust Browning and Mixon to carry the offense.
I think those flashes Jake shows are the reason why he's still in the NFL.