When your 2020 BMW X3 displays the P0305 code, the diagnostic approach depends on your engine. The G01 2020 X3 offers four-cylinder and inline-six options. P0305 is valid on M40i's inline-six but anomalous on xDrive30i's four-cylinder.
2020 X3 Engine Options
The 2020 X3 offers the 2.0L B48 I-4 (248 hp) and 3.0L B58 I-6 (355 hp in M40i). Only the inline-six has cylinder 5.
Diagnosis at 2020 Mileage
At potentially 50,000+ miles, spark plug wear is possible. Ignition coils can fail. Carbon buildup on direct-injection intake valves becomes significant. Check maintenance history.
Four-Cylinder
xDrive30i has a 4-cylinder where P0305 is anomalous.