It may be related to repository such as two below example: https://askubuntu.com/questions/579997/why-does-the-update-manager-say-check-your-internet-connection https://letsfoss.com/ubuntu-failed-to-download-repository-information/
You can first check whether you can disable some manually added PPAs. ** Summary changed: - Upgrade to 21.04 + Failed to upgrade to 21.04 (Check your Internet connection) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1933839 Title: Failed to upgrade to 21.04 (Check your Internet connection) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1933839/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
