Are you using File > Import or the Media Manager? Although, either approach should work as expected.
8-bpc, 16-bpc, and 32-bpc RGB Color Mode Photoshop files are supported with Premiere Pro on an Apple M1. So, it's probably worth taking a closer look at the PSD files.
Assuming you're not planning to import the PSD layers, you could try opening a few of the PSDs in Photoshop and using File > Export > Quick Export as PNG. Then try using File > Import to bring those in.
Since Premiere Pro doesn't print to paper, (that is, there's no File > Print), the DPI setting of the Photoshop document is ignored. Premiere Pro just looks at the width and the height as measured in pixels. So, 1920-by-1080 at 150 dpi is the same as 1920-by-1080 at 72 dpi which is the same as 1920-by-1080 at 300 dpi. The difference between what I just listed only comes into play when we choose File > Print in an application like Photoshop that prints.