Seagate Backup + Plus Hub 8 TB cannot recognize (engage) only Flashing light...

First is the Seagate drive plugged into the power adapter which is powered into a working electrical outlet?

Second, are you using the USB Micro-B USB cable which plugs into the back of the Seagate drive?

Try connecting the Seagate drive to another USB-C port especially on the other side of the laptop if you have four USB-C ports.

The USB-C to USB-A adapter/dongle you are using may not be compatible with the Seagate drive. Try using another brand of USB-C to USB-A adapter.

Once you get the drive working you should use Disk Utility to erase the drive as GUID partition and MacOS Extended (Journaled). Don't install the Seagate proprietary software as the included NTFS driver tends to cause problems especially after macOS updates/upgrades. Let macOS manage the Seagate drive.

Make sure to disconnect all other external devices from the computer & the Seagate drive's hub just in case they are interfering with the Seagate drive.

Did you get another USB cable with the replacement drive? If so try using the replacement cable on the off chance the original cable is defective or was somehow damaged by the power outage. Maybe even try getting a USB-C to micro USB-B data cable to eliminate the dongles if you don't have another cable to use for testing.

Do you have another drive to connect to the laptop to make sure the USB-C ports on the laptop are working properly and your USB-C to USB-A adapters/dongles are working? Even if other devices and the power adapter work it doesn't mean those USB-C ports are fully functional to access a hard drive. Maybe even try plugging the USB-C part of your dongle in the other way (upside down).

Are you using the Seagate proprietary software to manage the drive or do you have macOS managing the drive? If macOS is managing the drive, then reboot into Safe Mode to see if the drive works in case you have a software issue.

Do you have another computer you can use to see if the Seagate drive is working properly?

Also try an SMC reset and a PRAM reset since the power outage could have adversely affected your laptop. If you are using a surge strip, then try plugging the computer and the drive directly into the electrical outlet as the surge strip may have become damaged in the power outage.

Are you using the new power adapter with the replacement drive?

Did you first use the old power adapter to test the replacement drive? If so maybe the old power adapter was damaged in the power outage and in turn damaged the replacement drive. Getting another drive & power adapter should solve your problems.

Since you have verified other drives are working and you've tried different cables and dongles I think it is safe to assume the issue is with the Seagate drive and its power supply and not with the laptop.