I would like to produce something like that:
Does MathJax know a methode for \dotfill
?
PS: About MathJax says me
MathJax v2.7.5
using web TeX fonts
MathJax.js v2.7.5
TeX Input Jax v2.7.5
HTML-CSS Output Jax v2.7.5
mml Element Jax v2.7.5
MathEvents Extension v2.7.5
MathMenu Extension v2.7.5
MathZoom Extension v2.7.5
TeX/AMSmath Extension v2.7.5
TeX/AMSsymbols Extension v2.7.5
TeX/begingroup Extension v2.7.5
TeX/noErrors Extension v2.7.5
TeX/noUndefined Extension v2.7.5
tex2jax Extension v2.7.5
Chrome v120.0.0.0 — woff or otf fonts
No, MathJax has no mechanism for doing that. MathJax's internals are very different from TeX's, and it does not use the boxes, glue, and leaders that TeX does to make such a thing possible.