As the saying goes, get the right tool for the right job. Without going through the technicalities, I will make it short and simple. If you have a 4K projector, pls stick with a 4K cable with HDMI 2.0a/b specs. DO NOT, I repeat, DO NOT be tempted to get the latest HDMI 2.1 spec’ed cable as it may cause instability in the transmission of signal over time. This is less of an issue for TV owner. If you have an 8K capable projector with HDMI 2.1 inputs, then by all means and go for the latest HDMI 2.1 cable.
You may be thinking of “future-proofing now, but in fact, it is hurting the present”…