if the artists are using handheld mics and standing or sitting, assume they're singing live, if they're dancing and not using handhelds, assume they're lipsyncing.
I'm pretty sure I've seen idols with handheld mics lipsyncing, while headsets are often used by dancers/idols who can't use a handheld due to the choreography. Maybe headset quality tends to correlate a tiny bit more with the liveness of a performance, but it's far from a sure indicator either, I've seen numerous lipsynced performances with the bigger headsets, and live ones with the cheaper type.
As for the actual question:
Honestly I'm not sure about objectively how common live performances nowadays are, because I usually only watch individual stages and nowhere near from all groups; I only watch music shows themselves when Stray Kids are promoting, and even then I often mute that tab until they come on. (And SKZ are not really the group to be an indicator for lipsyncing, as they're adamant on singing live all the time.) But there are definitely live performances on each show. While a lot of them are indeed lipsynced, it's a massive stretch to claim all of them are.

