Hello, thank you for reaching out to Microsoft Q&A.
May I please know if you are experiencing the same error across different devices or web browsers?
You can try using an incognito/private browsing window in any web browser and then sign in to your Microsoft account online. If the error persists, please connect your device to a different Wi‑Fi network, such as a mobile hotspot, then clear your browsing History, cache, and cookies. See if you can sign in.
If the issue continues, try resetting your Microsoft account password once and see if that resolves the problem.