ser = pd.Series([1, 2, None, 4], dtype="Int64")

>>> ser.interpolate()
[...]
ValueError: Invalid fill method. Expecting pad (ffill) or backfill (bfill). Got linear

EABackedBlock.interpolate dispatches to EA.fillna, which doesn't handle method="linear". Getting this right probably will require implementing something new at the EA level.

Expected Behavior

pd.Series([1, 2, 3, 4])