VS Codium doesn't allow inserting snippets inside snippets. So first create your equation and then wrap it with $
for inline math or $$
for block.
Snippets are only active in Markdown files. If they do not show up edit your settings.json
file and add following code:
"[markdown]": {
"editor.quickSuggestions": {
"other": true,
"comments": false,
"strings": false
}
}