Hi,

Set notation “{}” is OK in TeX mode.
But it is missing in the output of the metafun code.
Here is an MWE.

It is same in two different versions.
ConTeXt  ver: 2021.01.17 21:42 LMTX  fmt: 2021.2.4  int: english/english
ConTeXt  ver: 2021.03.13 11:22 LMTX  fmt: 2021.3.14  int: english/english

\startbuffer[test]
label(textext("$\{a,b\}$"),origin);
\stopbuffer
\starttext
Let $A = \{a,b\}$.

\processMPbuffer[test]
\stoptext


Thanks.

Best regards,

Dalyoung