I appreciate your replies/insights. Ok. I have a LaCie 2big 8tb. Can I use that? I have other data on this. I’m unsure whether time machine would need a complete clean drive or whether it can just backup to the free space on it alongside my existing data. I don’t wish to partition the LaCie. If that’s possible that would confirm one way or another whether it’s a system or drive issue.
this is all a bit over my head.
As others say it is not recommended or good practice to put TM backup in the same partition but it will work for a diagnostic test.
I would be inclined to as someone said pick up a cheap spinner...could be a bus powered 2.5.