I've just bought a refurbished 2015 15" MacBook Pro Retina and have installed Big Sur and the latest version of Premiere Pro CC. I've just imported some A7iii 8bit 4K footage to edit and it's beyond choppy/laggy to the point of useless. I've tried 1/8 resolution, pre-rendering and even 540p proxies and it's always the same. The footage plays back fine in the source window but the moment it's in a sequence, premiere just haults completely.
I've included my Mac specs which seem capable enough to run premiere, and I've got an external SSD which I've tried saving the project/cache files to but doesn't seem to change anything.
Any support would be hugely appreciated. Many thanks, D