Apparently a 'newer macOS' provides digital signed PDF in Preview.
• Fill out and sign a PDF form in Preview on Mac - Apple Support
https://support.apple.com/guide/preview/fill-out-and-sign-pdf-forms-prvw35725/mac
While my antique Macs haven't been forced to perform manual
signed PDFs. Nor have they been sent to some PDF labor camp.
(Fillable forms of course have been available to macOS.)
According to the above Support article digital signing has been
available to older Mac systems; in some means or another since
High Sierra. Instructions differ across the system variants offered.
A newer Preview User Guide (Table of Contents) shows v. 11:
https://support.apple.com/guide/preview/toc/11.0
Seems the process on some models includes a force-touch trackpad
and/or a built-in camera (maybe an external for older installations.)
• How to create a fillable PDF | Make a PDF fillable | Adobe Acrobat
https://www.adobe.com/acrobat/how-to/create-fillable-pdf-forms-creator.html
Other results(?) appear in search:
https://duckduckgo.com/?t=ffab&q=writable+PDF+documents+through+macOS+software&ia=web
Your mileage may vary.
Good luck & happy trails! ☺︎