I no longer get oldstyle numerals in the math environment (ConTeXt  ver: 2021.04.29 ) with

\definefontfamily[mainface][rm][STIX Two Text]

[protrusion=quality,

expansion=quality, 

mode=node,

force=yes,

features={default, f:oldstyle},

]

\definefallbackfamily[mainface] [mm] [STIX Two Text]

    [range=digitsnormal,

force=yes,

features=f:oldstyle,

]

\definefontfamily[mainface][mm][STIX Two Math]

\setupbodyfont[mainface, 10pt]

\starttext

123456789

\m{123456789}

\stoptext