Custom domain Meet invites from mailbox.org with Proton MX: SPF/DKIM/DMARC?

I currently keep MX on Proton for incoming mail, but I’m considering mailbox.org Calendar + Meet and I want meeting invites to be sent from there info@mydomain.com. with reliable delivery. I can add SPF records, but the key question is whether mailbox.org can DKIM-sign outgoing messages as d=mydomain.com (and ideally align SPF/return-path as well) without switching MX away from Proton, so invites pass DMARC consistently; if this is supported, can you tell me the exact setup steps and DNS records (SPF, DKIM selector/value, DMARC) needed?

this was my setup in google workspace and it works there but I want to ditch google and am lost king to see if mailbox can replace it for me