SlicerVM (est. 2022) is already used for prime time, not "free as in beer" but has pretty reasonable individual plans that include all features. Shares the core code with actuated. (Creator of both speaking here)
Feel free to take a look and see if gives you a little more than the others you mentioned. If not no problems, I realise some folks prefer free stuff.
You might need it open source, the majority of the world doesn't care, like they don't care Windows is closed source, or like AWS is a "cloud" running somewhere else. Both of them are building blocks that made "the world better and more robust".
If you don't care that's fine. You go run the Claude Code "sandbox" and let it put your entire home directory on a public pastebin. Anthropic guarantee it will exfiltrate your data in the most secure way possible.
The rest of us want verifiable sandboxes which we can fix if they are wrong.