This site states this specific caution directly: Lion's Mane is a mushroom, so skip it if you have a mushroom allergy.
Worth reading "skip it" as a direct, unconditional instruction for this specific situation — distinct from the "talk to your doctor first" framing this site uses for its other medication-related cautions.
If you have any known mushroom allergy, avoid this product entirely per this site's own direct instruction, rather than assuming a small amount would be safe to try.