@EugW "...it's absolutely clear I do NOT need to upgrade my M1 16 GB Mac mini."
Earlier this year I needed to edit an hour and a half wedding video shot with 1080p cameras using an M1 mini 16/512, using FCP.
The footage was all on external 2800MB/s TB3 SSDs, but I used the m4v source files to edit as I didn't want to transcode to ProRes if I didn't have to.
Right at the start the mini crashed, and beach balled several times, then settled down.
So everything proceeded OK from then, with memory flatlining at max yellow, but never becoming red.
However there was a real problem throughout the edit, because the audio part of the timeline/project display could never update immediately, so throughout the edit I had to wait a second or so before I could get on with the next edit.
It was a real pain.
I think in part it was down to using external SSDs for the source footage, as when on the internal disk the lag was far less apparent.
I ended up leaving the source footage external, but keeping the FCP projects on the internal SSD.
512GB fills up really quickly with and hour and a half of edited timeline...
I was constantly having to clear older project snapshots off the internal onto the external SSDs.
And I wasn't even dealing with 4K.....
Moral: An M1 mini 16/512 is absolutely fine – until it isn't.
PS: M4 Pro mini on its way, with 24/1TB haha