ext drive connected to Netgear router via smb

It is very unlikely that the Netgear router can read HFS+ drives.

Also SMB is now deprecated in all OS.. and routers do not support SMB3 which is new standard.

Check if the Netgear router supports AFP or FTP.

And exactly what formats and what size disks.

Might help us if you give us the model of the Netgear.

What model of Netgear router do you have?

It is unlikely that the Netgear router will support Time Machine backups if that is what you are trying to accomplish.

And it is also an open question whether the the Netgear router will support Mac OS Extended (Journaled) disks. Check the documentation for the router to see what type of formats are supported at the USB port. (Mac OS Extended (Journaled) is also known as HFS+). Further, it is also possible that the router might support HFS+ formatting on a disk.....but not Time Machine.

As a test, reformat the hard drive again without encryption to see if things will work that way. If they won't work that way.....without encryption......then you will know that there is probably no way that an encrypted disk will be supported by the router.

In other words, no sense in trying to encrypt the disk (or the backup if you have trying to use Time Machine) until you can first get things working without encryption.

Sorry, I don't have this Netgear model to test.

If you have already tried this.........https://kb.netgear.com/21360/How-to-setup-Time-Machine-with-your-NETGEAR-router........I am out of ideas.

Your best bet would be to try to work with Netgear Support, since you have a Netgear router.

The nighthawk rax78

Does NOT support Time Machine.

It does apparently support HFS+ disks but the Mac does not support SMB1 (you need a NAS which supports SMB3).

It does NOT support AFP protocol which is the only other protocol that supports Time Machine.

Very few Netgear routers support Time Machine and most work poorly at best.

For now Netgear does not support any protocol that would allow you to even copy files to the disk as far as I can see from the manual.

TCP/IP, RIP-1, RIP-2, DHCP, PPPoE, PPTP, Dynamic DNS, UPnP, SMB, and L2TP

Have a play and try it from Finder.. but I really doubt you will achieve what you want.