They do, but I had to change my mail routing to use IPv4 to gmail because if I connect over IPv6 everything gets categorised as spam.

MX has IPv6:

~$ host gmail.com gmail.com has address 142.250.69.69 gmail.com has IPv6 address 2607:f8b0:4020:801::2005 gmail.com mail is handled by 10 alt1.gmail-smtp-in.l.google.com. gmail.com mail is handled by 30 alt3.gmail-smtp-in.l.google.com. gmail.com mail is handled by 5 gmail-smtp-in.l.google.com. gmail.com mail is handled by 20 alt2.gmail-smtp-in.l.google.com. gmail.com mail is handled by 40 alt4.gmail-smtp-in.l.google.com.

~$ host gmail-smtp-in.l.google.com. gmail-smtp-in.l.google.com has address 142.250.31.26 gmail-smtp-in.l.google.com has IPv6 address 2607:f8b0:4004:c21::1a

Yes. However SMTP these days is almost all just servers exchanging mail, IPv6 support is much less priority.