What is the network/other system you are connecting it to, 10G? Sell the MacBook and get a mini with 10G.

Have you tried reconnecting it to the synology or whoever it was before and see if it pops up then properly eject it

Get one large enough that you can backup the other drives also. By default it will exclude externals so just remove them from the list. Once you decide on the size, choose based on price, speed won’t really matter within reason.