In The Mandalorian we see an Astromech droid extremely similar to R2-D2 (but a different unit) stand up like a person with 2 arms and 2 legs. Can all such units do this? Specifically, I'm wondering if R2-D2 could. Canon answers are preferred but Legends is okay too.
It's not an astromech, or an R2 unit.
It's a droid of a different construction, that happens to have a similar upper shell and head area (in terms of shape and colouring), that rows a boat.
Darth Bombad has already shown that R2 units do not have such appendages.
There is no reason to think, after all this time, that R2-D2 could stand up like this just because a droid with a similar head could do so.
(Out of universe, I expect the similarity was intentional, to make us think the droid were an R2 unit for as long as its limbs were obscured by the rock.)