back up drives

External drives tend to be unreliable, so I have been using WD, Seagate and Toshiba external drives to also back up. For the past couple of months my Mac Pro (1 TB capacity - 377 GB free) is not recognising the external drives for back up. All three seem to have some fault!

For example, when I plug the Seagate drive to the usb, it shows up on the screen, and Disk Utility. Info shows that its capacity is 2 TB and available is 377 GB, used 1.62 TB. First Aid failed - First Aid process has failed. If possible back up the data on this volume. Click Done to continue.

Seagate's last backup is 29th November 2020.

Seagate Dashboard shows 0 MB free.

Time Machine(?) message states that the Backup Failed - TM couldn't complete the back up to the Seagate Drive. Files can’t be copied onto the backup disk because it is read-only. (How to make it Read & Write?) You may need to repair or erase the disk using Disk Utility. If the disk can’t be repaired, select a different disk for backups.

Latest successful backup: 29 November 2020

WD has 914 GB of 2 TB available

Toshiba has 86 GB of 2 TB available.

Any suggestions please?

Especially as all three drives have the same problem.