Dear IanDOE_21,
Thank you for reaching out once again.
Having tried signing-in with different browsers you still face the same issue.
Keep in mind that the error message you're receiving (related to the X-frame) suggests that there may have been too many repeated sign-in attempts that has probably led to Microsoft’s login page being blocked from loading inside a frame due to security settings. I would suggest that you retry after a 24H wait to see if this persists.
Furthermore, I would suggest that you try accessing Sway in incognito mode on your browser. To do so, open a new browser window > click on the three dots at the top right corner > login to https://portal.office.com and enter your Office 365 account details > click on the 9 dots at the top right > search and click on the Sway. This will completely take out browser related issues.
In case you are using a VPN or proxy, turn them off and try to sign in again since some network configurations may block authentication pages.
As previously asked, could you let me know if this issue affects others under the same Microsoft tenant as you? This will inform me on whether it is an issue specific to your account or your tenant.
Also, does this issue occur with other Microsoft 365 apps as well? Try signing-in to any other web app (e.g. Word online) and see if you encounter the same issue which will permit me determine if it is an issue with just Sway or the Microsoft suites.
If possible, try contacting the IT admin of your organization to check if Sway might have been disabled at the organizational level - How to find the organization’s administrator. The admin can check if Azure Active Directory (AAD) Conditional Access Policies to ensure that no policy is preventing access to Sway. For more information on conditional access, this link can be checked.
Thank you for your patience and understanding.
Sincerely,