Shiv Shankar Dayal schrieb am 24.01.2024 um 16:37:
> For example: \kern, \parindent and so on. Rephrasing the question, can
> LuaMetaTeX/ConTeXt compile
> plain TeX files. If yes, how can I do that?

You mix up two different things here.

1. Plain TeX is a collection of TeX macros like ConTeXt or LaTeX.

2. LuaMetaTeX is a program like pdfTeX or LuaTeX which provides commands
which are used by above mentioned collections to create macros.

Even though ConTeXt provides some commands which available in plain TeX
not all of the are supported which means you can't process plain TeX
documents.

On the other hand commands which are provided by the engine like
\parindent can be used in a ConTeXt document but higher level mechanism
like \setupindenting are the better choice.

Wolfgang