final means "final"

[cgpzs]

What Autosar rule requires that?

Relevant rules I can find:

Rule A10-3-1 (required, implementation, automated)
Virtual function declaration shall contain exactly one of the three specifiers:
(1) virtual, (2) override, (3) final.

Rule A10-3-2 (required, implementation, automated)
Each overriding virtual function shall be declared with the override or
final specifier.

So you can choose to use either "final" (perhaps redundant) or "override".