Can I make a $4,500 HAS tax deductible contribution if I received a W2 with $4,854 in box 12c (code DD)? TT allowed the HSA contribution and lowered my tax due by $300?

Code DD only reports the value of employer provided health care. By itself, it does not indicate whether that healthcare plan was eligible for HSA contributions or not.  You will have to check with your employer if you are not sure whether your healthcare was in eligible HDHP that allows you to make HSA contributions.

What is equally important is box 12 code W. If you make HSA contributions by payroll deduction, those amounts are recorded in box W along with any employer match. If you have employer contributions, that is included in your overall total and you have to be careful about making additional out-of-pocket contributions.

The limit for HSA contributions from all sources is $3500 if you were covered by single insurance, or $7000 if you were covered by family insurance. If you are ahe 55 or older, you are allowed an additional $1000 catch-up contribution.