Hi I got an email purportedly from Turbotax saying if I had more than one 1098 Mortgage interest form I may have left some $$$ on the table. Is this legit or pfishing?

Legit if it asks you to log into your TT account and fix it yourself. The program did have some glitches early in the season and some users may have a reason to amend. If this was fake they would ask you to contact them and trick you into giving up your PII.

They still can't calculate mortgage deductions correctly if you refinanced in 2020 and paid points (see my post in this forum -- they over-deduct in that case), but if you had a loan over the limit for deductible interest (or probably, also if you had multiple loans which add up to more than the limit), they require you to merge all the 1098s into one so they can get you the right interest deduction.

Otherwise, they calculate as if the combined balance was your loan balance and then reduce your interest based on that balance and the limit - which could massively under-deduct for many.