Yes that warning is standard practice for HomeBrew during a macOS βeta. Shortly before or when Sonoma is released it will be supported.

If you are using any network content filters like Little Snitch, LuLu, etc. this is a known issue. Disabling the content filter is the only solution to restore normal network connectivity at the moment until Apple resolves the issue.

Same here. Successfully updated from Beta 4 to Beta 6.

Same upgrade from ßeta 4 to ßeta 5 issue here on a M1 Mac mini external TB SSD drive. Even trying to update the external TB SSD using the full ßeta 5 installer from my internal SSD ended in failure. I guess unless Apple releases an updated ßeta 5 installer we can only hope the issue is fixed in ßeta 6. I did submit a Feedback report.

You can enable it using the menubar control center.

You can enable it in the menubar control center.

Unfortunately the installers are protected by the System Integrity Protection (SIP ) system. To delete the installers boot your Mac into Recovery mode (CMD-R) and open the terminal application from the menubar and execute the following command to disable SIP. csrutil disable Restart your Mac. You should be able to delete the installers. After you delete the installers boot back into Recovery mode (CMD-R), open the terminal application again and execute the following command to re-enable SIP. csrutil enable Restart your Mac and enjoy.