What model MacBook is this?

Sounds like you're describing the Mid-2010 White MacBook (Model A1342) — but likely one with some swapped or worn-out parts.

Here’s what stands out from your description:

• "About This Mac" shows Mid 2010 – that lines up with the final generation of the white polycarbonate MacBook.
• Display looks like a MacBook Air 13" – the A1342 had a plastic bezel with no front glass, similar in appearance to early MacBook Airs.
• Bottom case is a solid silver/aluminum panel, flat with no rubber feet or info printed – this is probably the original rubberized base that’s either worn off, removed, or replaced. The original soft-touch coating on those bottoms often peels and people replace them with aftermarket or donor parts.
• White keyboard and cream/white palm rest – matches the polycarbonate unibody design of the A1342.
• Running High Sierra natively – perfect fit. That model supports up to macOS 10.13 without patches.

So while it might look like a bit of a Frankenstein build, it's almost certainly a 2010 White MacBook (A1342). The mix of visual cues (aluminum-look base, Air-style screen) could be due to replacement parts or heavy wear and tear.

If you can get pics of the display bezel, side ports, and keyboard area, we can confirm it 100%. But from your description, I’d bet on the A1342.