@Nikolay Belykh Thank you for reaching out to us, reached out to CDX team to confirm this change, here is the response which I got:
MFA is being enforced and required for all CDX demo to enhance platform security posture. This is not something our team disable or change, as it is part of a global change to Microsoft demo tenants. Additionally, please note, customer access to demo tenants as described in the post is against CDX Terms of Use.
Let me know if you have any further questions, feel free to post back or raised a ticket a with CDX team directly as they don't work/reply on QnA platform.