Until you run out of hardware that can run an OS old enough that the old version of the framework works, sure. Even then, you may find it hard to add new dependencies without getting current on the framework, since most ecosystems require you to pick a winning version in the case of a "diamond" transitive dependency.

You can, and sometimes that's the right answer. Where it gets hard: security CVEs that need patching but the fix is only in the new major, transitive deps that bump and bring incompatibilities, hiring a contractor who doesn't know your locked version. None of those are insurmountable, but they're real tax.

the problem is that you have to keep all the artifacts around so you can keep building with the old framework. especially in the npm world that is incredibly annoying. my solution for javascript at least is to avoid build tools alltogether, and build the site in such a way that it runs without a build step only using frameworks that support that. since the code runs in the browser there are no security concerns because you can't trust that code anyways.