Policy from the CPU maker and willingness to cooporate by the Mobo manufacturer.

In this case, there was also a technical limitation in the form of BIOS ROM chips that were too small to hold a BIOS that supports newer CPUs.

The socket on your mobo has to be compatible with the cpu socket type.

Also your power supply should be up to snuff for any upgrades.

AMD has given its word to support AM5 til 2025

AM5 was released with the 7000 series CPUs. 8000s are absolutely going to be supported, and there's a very high chance 9000 will be supported as well. I believe AM4 was supported for 4 generations of CPU.

Chances are you won't conclusively know which CPU is supported until they are released, but to keep the odds ever in your favor you should pick a higher generation chipset. Unfortunately, it looks like only the 6xx generation are released at the moment so there's not much choice.

Generally it's the mobo chipset that determines which CPUs are compatible. Often the chipsets are compatible with two generations of CPUs, that was the case with H6xx from intel, i got one with an alderlake cpu amd could upgrade it a year and a half later with rocketlake. The mobo OEM needs to support this in their uefi/bios