Though this mentions Nemo, I'd actually wiped Mint in favour of Pop OS by the time I found this, but the same applies to Files which is the Pop OS version of Nautilus
So what worked for me was to go to +Other Locations and totally ignore the supposedly handy direct Network links to my unraid server and other devices on the network. At the bottom of the Files window there's a field with "Enter server address" into which I put
smb://nameofmyunraidserver.local/nameofshare
I find it very odd that these things don't just work OTB between two machines running Linux (NFS didn't work either) and all the tutorials I could find target setting up Samba to share a folder on the machine you're on, rather than to connect to a share on unraid. If I've just missed a straightforward quality tutorial despite hours of searching please post a link!
This one from Matt Hartley was the best I've found so far:
