Last time I did this, I printed, signed and sent only the last page, which had the signature on it. They rejected it because I didn't print and scan the entire document.

I had success with the famous scanner.sh gist (https://gist.github.com/andyrbell/25c8632e15d17c83a54602f6ac...):

  $ convert -density 90 input.pdf -rotate 0.5 -attenuate 0.2 +noise Multiplicative -colorspace Gray output.pdf

(convert command -> requires ImageMagick)

I have used https://lookscanned.io/ with success, but you mileage may vary.

PDF annotation with a cheap drawing tablet works well enough for my insurance and others, and is a lot more convenient.

If they'll accept a PDF at all, just using a digital signature annotation in Mac Preview is sufficient for every use case I've found. The ones that won't accept this generally require physical hard-copy, not a scan.