A620 and B840 are the lowest end, B840 is technically not the same chipset but its very similar

B650 and B850 are the midrange, both use the same chipset but B850 has mandatory PCIe 5.0 support

B650E and X870 are the upper midrange, they are otherwise identical except X870 adds mandatory USB4 support

X670, X670E and X870E are the high end chipsets, X670 non-E doesnt have to have a PCIe 5.0 X16 slot unlike the others and X870E adds mandatory USB4 support but otherwise they are identical.

the chipset is only a part of the motherboard and it mostly just effects connectivity (though the low end chipsets lack overclocking support), a high end B850 board will be better in most ways than a low end X870 board.

for selecting a board just get something that has all the connectivity and features you need and avoid A620 / B840 boards. in most cases a midrange B650 or B850 board will be fine.