You are using BOTH monitors for the gameplay, or just one for gameplay and the other for browsing, utilities, etc?
Either way, if you have a 144hz 4K monitor, and want to play at ultra settings, then yes, it would very much make sense to buy the best card you can afford (And actually GET) from the RTX 3000 series. An RTX 3070 gains you nothing, so that isn't really an option, but an RTX 3080 should have more performance than your current card and an RTX 3090 should offer a very significant increase in capability. The only reason the 2080 ti was a good choice for 4k gaming is because it was the best card you could get for it, and now, it's not, so it's not a great option to remain with if you are looking for more than 60fps (If you're lucky, on some games, at high or ultra settings. Hell, even medium on some really demanding games without moving some sliders to the left.) on 4k without some reductions to some settings.