It's nonsense.
The slim nose. Almost everyone went to it. Probably only Ferrari and Haas will stay with wide nose, and probably only because of limited rules.
Yes, they chose to make identical copy, but of the best car on the grid. Who wouldn't?
Front wing was also identical on reveal of RP20, but they slightly changed upper element.
Those things. Everyone went for horizontal ones, except Williams. But they not yet revealed this year's car.
Yes, they again chose to be identical to Mercedes. But who wouldn't if they can?
Boomerang wings on RP20 was identical to W10, but they changed it during the season on their own design. They still have their own design.
Sidepod inlets. Mercedes was the last to go on high inlets. RP20 had middle inlets, which is a copy of W10. But RP19 had high inlets, before Mercedes, so AMR21 high inlets can't be a copy of Mercedes. The shape of the sidepods looks different too.
Engine cover. If you look at shark fin area of RP19 car (before a copycat RP20) you can see it's similar shape as Mercedes. Which means they have similar packaging. And they have it before they decide to copy Mercedes. Which is logical with same engine. And they are using it for years. It's also logical that McLaren can't have the same shape in their first year with Mercedes engine.
With engine covers shrinking every year, it's logical they went to almost the same shape.