learn how to use/repair/program old computers, the pre-ROHS stuff that had large, simple components you could solder by hand, with leaded solder that doesn't grow dendrites
learn BASIC and C and ASM for the 8086 and Z80 and 68000, learn everything you can about microcontrollers so you can harvest and repurpose parts from everything around you (Intel 8051s are in goddamn everything)
build and run old versions of Linux on PCs with less than 1MB of RAM that have been retrofitted with tiny amounts of flash storage
in the event that new manufacturing and availability of new hardware is constrained to industrial applications only or worse, completely unavailable, those are going to be the machines that will actually run for decades
learn how to use/repair/program old computers, the pre-ROHS stuff that had large, simple components you could solder by hand, with leaded solder that doesn't grow dendrites
learn BASIC and C and ASM for the 8086 and Z80 and 68000, learn everything you can about microcontrollers so you can harvest and repurpose parts from everything around you (Intel 8051s are in goddamn everything)
build and run old versions of Linux on PCs with less than 1MB of RAM that have been retrofitted with tiny amounts of flash storage
in the event that new manufacturing and availability of new hardware is constrained to industrial applications only or worse, completely unavailable, those are going to be the machines that will actually run for decades