This is the first time I've heard of Deno so I'm only going by their Security & Permissions doc page [1], but it looks like the doc page at the very end recommends using system-level sandboxing as a defense in depth. This suggests that Deno doesn't use system sandboxing itself.

To me this is a bit alarming as IIRC most app runtime libraries that also have this in-runtime-only sandboxing approach are moving away from that idea precisely because it is not resistant to attackers exploiting vulnerabilities in the runtime itself, pushing platform developers instead toward process-level system kernel-enforced sandboxing (Docker containers or other Linux cgroups, Windows AppContainer, macOS sandboxing, etc.).

So for example, .NET dropped its Code Access Security and AppDomain features in recent versions, and Java has now done the same with its SecurityManager. Perl still has taint mode but I wonder if it too will eventually go away.

[1] https://docs.deno.com/runtime/fundamentals/security/

Deno is a V8 wrapper, the same JS engine as Chrome. Vulnerabilities are very common there, not necessarily because it's poorly designed but more because there's massive financial incentives in findings them.

This plus what you mentioned is why I would never trust it to run arbitrary code.

Now in the context of yt-dlp it might fine, google isn't going to target them with exploits. I would still prefer if they didn't continue to propagate "DeNo iS SaFe BeCauSe It HaS sAnDbOxInG" because I've seen projets that were actually executing arbitrary JS rely on it thinking it was safe.