Can I apply for a tax credit on 20% non reimbursed part of my extended benefits even if the total expenses out of my pocket fall below the 3 % of income threshold ?

In order to claim medical expenses, you need the total amount of expenses which you have paid to be over 3% of your net income. The 20% portion not covered by your plan must be above this threshold in order to have any effect on your return.

https://turbotax.community.intuit.ca/replies/2647779