Is it appropriate to build an ITX workstation today?

I haven't built a PC in years, so you could say I'm quite behind the times. I'm looking to upgrade from a full tower (total refresh, from scratch) and I must say that these SFF builds have attracted me.

It seems that the SFF community uses their PCs primarily for gaming or content creation? My use case is quite intensive and really requires the best consumer hardware out there to work at a reasonable pace. I am involved in film restoration and use software such as DIAMANT suite, PFclean, TOPAZ VEAI, iZotope RX, Pixbim colouriser and Premiere Pro. I'm expecting something like a flagship consumer processor (like a Core Ultra 9), 128GB RAM (yes, I've found ITX boards that support this), RTX 5090, 8TB storage, etc. Only need the one PCIe expansion slot for the graphics card.

Now, I've heard that mini-ITX builds still compromise performance for aesthetics, and that you may need to undervolt your CPU (especially for the top-end processors). How true are these claims today? Would a custom loop with waterblocks for both CPU & GPU, along with a good airflow case like the Corsair 2000D, make a noticeable difference? I suppose the main question is, is an ITX build right for me?

My budget for this build is ~$12K USD including the monitor (doesn't have to be that much, just the max I've allocated).