they had to segment it, agesa code is big, older mainboards had 16MB bioses, for full CPU support you need 32MB bios
so there are currently two agesa versions maintained, agesa V1 (for CPUs up to zen2) and V2 (for CPUs from zen2 onward)
both are 16MB, with 32MB bios you can run both of them and can run it with any CPU u want, but with 16MB bios, you can fit in only one agesa version, if you switch to V2 agesa, then youll loose cpu support which predates zen2
mine asrock x370 gaming x has bios 6.12 with agesa combo-am4 pi v2 1.1.0.0 dated december 2020 which supports zen 3 (vermeer)
its not like those bioses with agesa V2 for zen3 doesnt exist, just ask asrock and theyll send you one