Is there a maximum amount of medical deductions that can be applied?

No, there is no "maximum" per se, but you cannot reduce your income below 0 with medical expenses.

Okay, it’s confusing because I’m putting in x amount of medical write offs buts it’s only deducting 8k less than what I’m putting in?

That’s most likely a factor of the program deducting a percentage of your adjusted gross income in computing your deductible medical expenses.

In 2019, the IRS allows taxpayers to deduct the total qualified unreimbursed medical care expenses for the year that exceeds 7.5% of their adjusted gross income.

Please see the TurboTax Help article “Can I Claim Medical Expenses on My Taxes?” for more information.