[nota]

IF THE iMAC is newer

It should have an m2 slot
now apple the SOBs that they are use a style m2 NOBODY else uses
you can get an adapter to use a standard m2
anyway the new m2 drive is way way faster then the older SShd
it should be simple to add a m2 but apple needs the imac taken apart

and you should have your old spin HDs in raid to copy not the stupid time machine [wife has one]
yes they sort of ''work'' but 90's level tech now as they copy everything ever time stupid when all is needed are the things changed
not a complete copy of everything every time