In Don’t Disable Form Controls, Adrian Roselli explains that, while it sometimes can be ok to disable buttons, it's never ok to disable submit buttons (or any form fields):
Telling authors not to disable submit buttons is too narrow. Authors should not disable any form fields.
Hidde de Vries (@hdv@front-end.social) is a web enthusiast from Rotterdam, The Netherlands. He currently works on accessibility standards for the Dutch government (views his own) and is in the W3C's AB. Previously, he worked for Mozilla, W3C/WAI, national and local governments, Sanoma Learning and others as a freelancer. Hidde is a public speaker (all 79 talks). In his free time, he works on a coffee table book covering the video conferencing apps of our decade.