There's reasons to be skeptical of particle accelerators as a frontier of physics, Sabine Hossenfelder has expressed this quite well, it's unlikely to help us learn anything CERN hasn't already and it seems increasingly that when theoretical physics doesn't agree with experimental reality, they aren't revising theories or looking elsewhere but assuming the theory was right we just need higher TeV to do it this time - like SuSY. This new potential accelerator sounds basically like they just want to do more collisions with higher TeV, but at least they state they can study the Higgs a bit better with it besides trying to search for more particles...

It's frustrating because basic research is so underfunded and it can feel very zero-sum that yet another particle accelerator is gonna get built and it almost certainly will NOT discover anything new. When they proposed CERN, they talked about how they may never need a higher energy accelerator again. There's no off button for this particular flow of experiments when, at this point, we really have to be discarding some entire avenues of questioning because they just aren't matching up with reality.