RE: Dynamics 365 CRM portal meets WCAG 2.1 accessibility standards or not
I don't believe they retrieve official WCAG 2.1 certificate, and actually, I'm not sure such certification exists.
CRM Portals surely satisfy absolute most of WCAG requirements (99%), including Voice Readers, Keyboard accessibility, all the descriptive elements of the tags and meta tags and so on.
Standard Blue Theme probably will fail to comply enhanced contrast requirements on any possible device, but its common problem for this topic.
If you need something "official" - you need to contact Microsoft directly :)