I came here to comment the same [https://www.cnx-software.com/], their comments section though is pretty decent, there are usually 10+ comments (decent quality) on posts for popular MCU/SoC/embedded software/other popular releases.
(disclaimer: I run the Interrupt community at interrupt.memfault.com)
Closest I've found is the "hardware" tag on lobste.rs (https://lobste.rs/t/hardware), though it is not super active. There's also the /r/embedded subreddit, though the main moderator is pretty terrible so it hasn't always lived to its potential.
We'd be keen to host something on Interrupt, if there is interest. Come join us in Slack (join: https://interrupt-slack.herokuapp.com/) if you'd like to chat about it!
