W2 form Box 1 empty but boxes 3-6 have data

I'm retired. I left my last company August 2022. I received a W2 form them for 2023 that has an empty box 1 but has data in boxes 3, 4, 5, 6.

Because of the empty box 1, I cannot efile. I'm asked to mail the return instead.

Why did I get this type of W2 form, the year after I left the company?

Thanks