Standard Notes has an unfortunate business model. Instead of charging for the convenience and security of syncing your stuff on your behalf (which is the model of Obsidian, Joplin, and Bitwarden), it wants to sell you a Markdown compatible note editor that
They didn't write
They don't maintain
Can just sit on your phone/PC
This isn't just true for their markdown editor. Most of their editors are wrappers for code that other people made, sometimes last updated years ago.
Fun trivia: Filen, the E2EE cloud storage service, actually implemented "notes" that include the rich text ones free of charge.
Personally I'm not a huge fan of the "everything under one roof" model regardless... You might pass up perfectly good services that cost less or are even free.