I decided to try to run Cloud9 on an ARM server ("Graviton"). I created an EC2 t4g.medium instance and a key, made sure I could SSH into it as expected (no problem), and then created a Cloud9 SSH environment. It mostly seemed to install without issue aside from a mild complaint about Sqlite. When I opened the IDE, it was perfect. Terminals worked as expected, files saved, autoformatter autoformatted and the world was good.
Every subsequent time I have opened the IDE, however, it has just given me a loading spinner. After a lot of Googling I noted that this pattern has been seen before. I tried installing tmux, but that had no effect. See screenshot:
According to this document, graviton isn't officially supported: https://docs.aws.amazon.com/cloud9/latest/user-guide/ssh-settings.html#ssh-settings-requirements. Other things that might cause it to fail are if the instance isn't publicly accessible on the internet (ie on the public subset with port 22 open, or connectable through a jump host). Also, you'll probably want a security group that only allows traffic from Cloud9; see here: https://docs.aws.amazon.com/cloud9/latest/user-guide/ip-ranges.html.
Additionally, I found the Cloud9 installer doesn't mention needing to install
gcc-c++in addition togcc.Because I don't want my machine on the public subnet, I'm giving up and waiting until this is supported. But I hope this might give you some useful information.