Part 1 Microsoft Reserved 134 Mb
Part 2 Basic Data NTFS 467 Gb
Part 3 Basic Data NTFS 467 Gb
Part 4 Linux 1 Mb
Part 5 EFI System FAT 538 Mb
Part 6 Linux file system 1TB
Is this normal and what should I do about it?
Timeshift seems to be using Part 6, though I have a suspicion that DejaDup refuses to use it
Part 6 is presumably the phantom 1 Gb drive I keep coming across?
Well, it seems that it only wiped You 240Gb Sandisk Drive. If you sure that You don't need anything from the 2TB Hard Drive, You could delete all the Partitions.
The NTFS Partitions should be from Windows. There stands ''Programs'' on one and ''Data'' on the other. And the ext4 is for Linux. When You choose Your 240GB Disk what Partitions are shown to You?
Okay, that looks good. There is the EFI-Partition and the ext4-Partition.
So, from this, I would think, You can delete Your 2TB Drive. If the ext4 Partition on the Drive is from Your timeshift Setup, You should of course not delete this. But the others shouldn't be a Problem I guess.
Well, when You have used that for Dual-Boot, the ext4-Partition could be the Linux OS what You have taken for create the Dual-Boot.
You could simply take a Look in the Timeshift Settings how it is set up and where it saves the Back-Ups's. Because I don't use Timeshift, I can't tell You where to find that. There You must look by Yourself.
I've already checked - it backs up to this drive. Actually, I've just restored a backup from it.
If I delete the other non-Linux partitions, what should I format them as and should I add them to the Linux main partition on the drive by repartitioning?
When You only use it for Linux, simply take the ext4 Format. It could be that it so automatically connects - but don't have to. Maybe You do first delete and format it.