One workaround is to utilise web hosting services and RSS feeds. I found this quite quick to set up. (I am not super tech savvy). It does create a webpage though, which you may not want. It essentiall looks like Obsidian → GitHub and Vercel → RSS feed → Mastodon.
You will need the following:
Obsidian Digital Garden plugin. The docs here will set you up up to the RSS feed. The plugin allows you to publish from your vault.
GitHub account to host your vault remotely, pushing via the digital garden plugin.
Vercel account to convert your vault to a Vercel hosted web page, and create an RSS feed. You create your GitHub repository from Vercel.
EchoFeed or MastoFeed to push any new published vault notes from your RSS feed to Mastodon. I prefer EchoFeed because it has a few more options, has just been released, and the creator Robb is very active and engaged with its users.
In Obsidian I have set up a macro using the QuickAdd plugin and templates to quickly create a note that finds its way to Mastodon.
I’m still tickering with this process but if you want to follow along here is my VERY drafty published vault and Mastodon account.
Keen to hear of similar setups or straight to Mastodon options too. I feel like there’s a lot of movement in this space right now.