Will I receive my amended return check via deposit or check in mail? I amended approximately 3 weeks ago due to qualifying for credits, but haven't received anything?

check in mail. 

Expect the amended return to take 6 months or more to process in this unusual time we are experiencing at this time.  Once a week you can check this tool to see a progress report :  https://www.irs.gov/filing/wheres-my-amended-return

The IRS does not make direct deposits for amended return refunds.   They will mail a check to the address on your tax return.  And as stated.....it will take months.