It's hard to imagine a tool designed to support research doesn't support footnotes in markdown. This one issue will keep me from updating my subscription. It is extremely important.

I imagine the creators would consider this feature to be redundant for hyperlinking, and writing papers in TheBrain not the primary goal. But Wikipedia is built on the same card concept, and I agree breakout references are sometimes needed.

Here's MediaWiki implementation: https://en.wikipedia.org/wiki/Help:Footnotes

## This markup:
This is page content.<ref>''LibreOffice For Starters'', First Edition, Flexible Minds, Manchester, 2002, p. 18</ref>
...
{{reflist}}

## Then creates this result:
This is page content.⁽¹⁾

...
LibreOffice For Starters, First Edition, Flexible Minds, Manchester, 2002, p. 18

This is one of the few things (apart from PDF) that TheBrain does not allow. It is a great restriction to those writing papers.