I check "maximum contribution to Indiv. 401k" and Turbotax then calculates 64500 for me, but when I go through the federal check it says I'm limited to 19500. Why?

[null672]

I then try 32000 and I get the federal check of 19500 as well. I am over 50 so I at lest get 26000

[Critter-3]

If you are referring to a SOLO 401K  then don't get the employee and the employer's  maximum allowed  contributions mixed up ...  https://www.fool.com/retirement/plans/solo-401k/contribution-limits/

You are asking from TT Live, for which you paid extra. Please contact a rep.
https://ttlc.intuit.com/questions/4124827-how-do-i-connect-with-a-tax-expert-in-turbotax-live