No, I don't own a scanner. Your only instructions were to save a file from PSP with uncompressed selected as the compression method. I took this to mean that this error occurs with all uncompressed TIFF files even those produced by PSP. So I took images from several devices, including several RAW files, opened them in PSP, saved as an uncompressed TIFF file 16-bit and when i reopened them there was zero difference.
Using the example file provided by @Raymura so that I am working with a scan. Opening in PSP I see the issue described. Using that scanned image I tried multiple methods.
1) I opened the original in psp2021, Camera Raw opened - setting highlight recovery to balanced, full shadows, and reduced brightness. Saved as Tiff uncompressed, the file loaded exactly as saved without camera raw.
2) I opened a copy of the original in Photo Viewer, rotated, rotated back, saved. PSP opened in camera raw
3) I opened in Windows 10 Photos, saved a copy - PSP opeend in Camera RAW
4) I opened in PSP8 - Saved as uncompressed TIFF - PSP 2021 opened exactly as saved without camera raw.
5) RAWTherapee - opened and saved as uncompressed 16-bit TIFF - opened properly in PSP 2021 without camera raw.
So those saved in editors as uncompressed opened just fine.