I’ve seen it in mine too but it looks tricky to get to. My version of the manual says this...
I copied and pasted it below.
IMPORTANT The oil dipstick in the engine compartment, on versions with 2.2 JTD engine,mustbeusedONLYiftheoillevel sensor is faulty. The latter condition is
indicated by the symbol which will
appear on the instrument panel.
The manual engine oil level checking procedure must be carried out, when necessary, on a cold engine only.
Never attempt to carry out the manual engine oil checking procedure (using the dipstick) with the engine hot. Contact with the surrounding hot engine parts could cause burns.
This operation is permitted only for the time actually needed to restore correct operation of the oil level sensor at an Alfa Romeo dealership.