In general, I'd recommend removing the previous layer before adding a new one for most projects.
its possible but the tile has to be well adhered and very flat. I have discovered this in previous houses and it looked like they used floor leveler to smooth out and fill grout lines. usually better to demo if possible.
Remove the old flooring first. Otherwise you will have an awkward transition and tripping hazard to all adjoing flooring.
Your best bet is to remove the old first. If anything happens to the tile if you cover over it, it’ll damage the new which will be more costly in the long run. Too, having a flooring level change is a tripping hazard.