Hi @freethefrail, this is a known issue with the system that Obsidian is build upon. See this forum for more details: https://forum.obsidian.md/t/macos-text-replacement-doesnt-work/
There is a feature request for it but since it is an Electron limitation, it probably won’t happen anytime soon.
There are great workaround though: Espanso as an app or the Obsidian plugin.