There is definitely isolation. In theory (if containers worked perfectly as intended) a container can't see any processes from the host, sees different filesystems, possibly a different network interface and basically everything else. There are some things that are shared like CPU, Memory and disk space but these can also be limited by the host.

But yes, in practice the Linux kernel is wildly complex and these interfaces don't work quite as well as intended. You get bugs in permission checks and even memory corruption and code execution vulnerabilities. This results in unintended ways for code to break out of containers.

So in theory the isolation is quite strong, but in practice you shouldn't rely on it for security critical isolation.

The Linux kernel recently became a CVE numbering authority. That means that there are now tons of CVEs coming out but the overwhelming majority aren't easily exploitable. They can be rated pretty high with no actual impact. Furthermore, a lot of them require a very specific setup with specific kernel components. It is best to look at the exploitablity score and the recommended CISA actions.