regards to Garuda I'm not sure on the 787 as they are going ahead with an order for 14 A330-900neo.
The previous plan before this COVID that I heard from them was to weigh in option for All Boeing Fleet for Garuda and All Airbus Fleet for their low cost subsidiary Citilink.
Garuda in the process to release all their CRJ and eventough there's talk in Media before that they will transfer all their ATR to Citilink, but the new CEO seems just want to get rid of ATR too.
Some people will think why differentiate two Airliners brands in one group, as Garuda as group will still have to sustain both Airbus and Boeing fleet anyway. However Citilink and Garuda is legally different entity, thus their book will be different. Thus, even they are one group, but the cost structure for each book will be different.
Off course again as I mentioned before on my previous post, this plan being considered before COVID situation and before New Management coming in.
As this COVID, or after the COVID, I don't even sure which way they're planning.
Citilink already operate A320 and begin inducting A330Neo. They want to follow Air Asia model of operating low cost for regional and long range flight. Garuda 787 talk being put by previous CEO when they're cancelled the MAX8 order, as part of Renegotiation with Boeing.
With current situation, I'm even not sure they will going to take all their A330Neo option, as seems all Airlines now all over the world rethink their fleet strategy development.
However
if the airline industry condition improve faster, it's also a sensible strategy for Garuda's as Group differentiate their long range fleet with 787 on Garuda and A330Neo on Citilink. Just like they already differentiate the Short-Medium range fleet with 737 on Garuda and A320 on Citilink.
In fact some Investment Analyst put assessment that in support Future Garuda should only operate All Boeing with 737 and 787 while Citilink with All Airbus with A320 and A330Neo. Thus they think Garuda not only has to ditch CRJ and ATR (as Garuda's new Management seems agree on that), but also ditch 777.
All this as example how after COVID situation, Airlines
will and should continue simplified their fleet. I agree with your assessment that it will be difficult for Boeing to persuade Airlines that already used A321, but in the same time Airlines that already used Boeing will think twice to move to Airbus. Which why I do still think Boeing will still try to come out with their middle of market answers soon, because they can't let all 757 customers when to Airbus. It will be very difficult for Boeing to attract them back, once they move to Airbus.