Import says "save with maximize capability" even though I already did

"However in PS under File handling I have save with maximum compatability set to "always".  I have also tried changing it to "ask" and choosing to save w/ maximum compatibility after it asks, but regardless of which way I do it I still get the error when I try to then import that .psb into lightroom."

Note that there is a seven-year-old PS bug where PS never changes the compatibility of an existing file despite changing the save options. After changing the save options, you have to save a new copy of the existing file, and the copy will get the new options.

If this doesn't help, upload a problem PSB to Dropbox or similar and post the sharing link here. I can poke inside the file to see if it actually has a compatibility layer and narrow down where the problem might be.

You might try using the free DNG converter and try importing again:

https://helpx.adobe.com/camera-raw/digital-negative.html#downloads

What size is the file? This may be a different error. Lightroom Classic supports PSB now, but it still has file size limits. A file must be less than 500 Megapixels and less than 65,000 pixels at the longest side.