Sadly, I disagree. If he keeps Ronaldo it solves one problem, but will create so many more & on balance I think ETH knows this. Do not underestimate what damage Ronaldo will do within the dressing room, together with that other example of Portugese petulance (Bruno Fernandes). I bet the new manager will have already noticed a change in mood: togetherness and team cohesion on the American trip vs stress and tension now they are back the UK. This is definitely the first real test for ETH: he needs to stand up for what is right for the club - get Ronaldo out and use the money saved to buy a replacement, even if it it means taking a risk on a player from from division one or the championship.
This would have the added advantage of indicating to a certain member of the board, that he is not the boss anymore, Erik Ten Hag is. Come and watch the matches, be a club ambassador by all means, but as regards actual decisions which have real consequences leave it to the new guy, he isn't a relatively inexperienced manager like OGS and it isn't 2012 its 2022.
That phone call last August to persuade Ronaldo to come back was not the first of Sir Alex's big mistakes (there is a dedicated thread on this elsewhere) but it has to be the last. What was the ex-manager even doing at the ground at the same time as Ronaldo's crunch talks earlier in the week? The telegraph reported it as unconnected, a pre-arranged board meeting - so the timing was just a coincidence then? Man Utd. have two GOATs who just don't want to quit and who want to remain in the spotlight - sadly they both risk tarnishing their reputations, one needs to go and one needs to stay in the background. To not do so would be dealing the new manager a bad hand from the start and he ain't gonna get four years to become a success - 18 months tops*, he should be allowed to start those 18 months without all this baggage to deal with because signing Ronaldo was not his call.
*P.S. If ETH's contract is similar to that given to Moyes, Van Gaal, Mourinho & Solksjaer he might have the must-reach target of Champions League qualification to meet. That is going to be very difficult, because the new rules enabling the top-five to qualify don't come in till 2024 and even that raises another worry: I bet by 2024 Newcastle will be a top-5 contender.