Also, TNG, DS9, VOY and Lower Decks establish that multiple uniform variations are worn at the same time. So people serving in forward areas or ships-of-the-line wear either the TNG (season 3-7) variant, the DS9/VOY variant, the grey wartime ones, and those serving support roles can wear the Lower Decks uniform. Beyond just that, if Starfleet is like the US military, the commanding officer of a duty station can set the uniform that'll be worn. In a fleet spread across 8,000 light-years, there could be a lot of variations based on the preferences of those in charge.