"Doug" wrote

Can a pilot who owns an amphibian that is no longer capable of landing
on the water get a flight review in the amphibian?
Yes, but it will not include privileges of flight in on water.

I think that you missed this one Doug.

(c) Except as provided in paragraphs (d), (e), and (g) of this section, no
person may act as pilot in command of an aircraft unless, since the
beginning of the 24th calendar month before the month in which that pilot
acts as pilot in command, that person has—

(1) Accomplished a flight review given in an aircraft for which that pilot
is rated by an authorized instructor and.....

One Flight Review is good for all aircraft for which the pilot is rated.
There is no requirement for different Classes.
The Flight Review can actually be accomplished in an approved simulator
under certain conditions.
There is a separate requirement for a PIC check for aircraft certificated
for more than one pilot.

Bob Moore