I think something interesting happened when computers became mass-produced - before which, they were built as one of a short production run, before which each one was a unique design and implementation.
For my own definition of computer - something which performs computation - I’m quite keen on recognising the programmable calculators. Two notable early ones are Olivetti’s Programma 101
and the not-entirely-unrelated 9100 from Hewlett-Packard (“due to the similarities of the machines, Hewlett-Packard was ordered to pay about $900,000 in royalties to Olivetti”)
Both are great marvels of technology and engineering. Another machine which must be remembered is the amazing MCM/70, a portable/luggable machine, self-contained, with a one-line display and which swapped to cassette tape, and which offered APL as the programming language and user interface.
https://www.xnumber.com/xnumber/MCM_70_microcomputer.htm