The solution posted above by @Cathy_Sarisky works well. I’ve been using it for 6 months with hundreds of footnotes without an issue. A significant proportion of my newsletter readers click through to the Javascript-enabled browser version to read it.
I periodically include a callout that reminds readers that the {{3}} squiggle-enclosed text are footnotes.
I compose offline in Obsidian, then process the Markdown with a perl script to change the embedded footnotes to format them for the solution @Cathy_Sarisky uses … this allows me to simply type some text {{456 Here is a footnote}} and have it correctly converted to some text {{1}} with the footnote added at the bottom of the page.
I use squiggles (braces??) rather than [[square brackets]] as Obsidian uses these for internal linking.