Can't track my 2021 federal refund

[zi4]

Hi, I mailed both my state and federal tax returns during the first week of March, and I already received my state tax return weeks ago, but I still can't track anything on IRS website about tracking my refund, and it's more than 6-week. I am not sure if there is anything wrong with my return, and is it because my status changed from nonresident alien to resident alien last year? What should I do? Thanks for any useful information and suggestion! Thank you

[Bsch4477]

Mailed federal returns may take months to process. Be patient. 

[xmasbaby0]

https://www.businessinsider.com/taxpayers-filing-paper-returns-wait-6-months-tax-refund-2022-4#:~:te...