Hi list! Nesting radicals in LMTX give a funny font size compared with
LuaTeX, which gives the correct output. I cleaned the cache, just in case.
I attach code and outputs. Thank you in advance.

\startTEXpage
\startformula
a_{2n} = \sqrt{2-\sqrt{4-a_{2n}}}
\stopformula
\stopTEXpage

Jairo :D