Deductions & credits

Thanks @ColeenD3, this explains.

Question1: I read instructions for line 12b. Please see the screenshot, it is about cash expense. This means we can cover miles also. Right? At what rates can we convert miles to cash?

Question2: I realized I have some 2020 expenses also which I could have deducted? Can I take 2020's deduction this year? Will this increase chances of audit? Not sure if I have enough records for 2020 expenses, should I first find them and then only take 2020's deduction?