I’d say it depends and it’s mostly just a theory that applies in some cases (like with kernel, critical infrastructure, server software) but usually desktop stack in LTS is just stinky old, which doesn’t make it any more stable, in some cases less stable.
Usually desktop environments are locked to some old versions and in theory fixes should get applied by the distro maintainers. In practice, actual developers behind desktops long moved on and don’t support it, bugs can only be fixed by huge code rework and it can’t be easily applied on top of old version (or can introduce new bugs and require testing). You end up with bugs that were fixed in upstream like 2 years ago and you will only get it improved upon new LTS upgrade cycle.
For example, LTS absolutely sucks for Plasma, because for last few years, each version is less and less buggy. On Debian/Ubuntu you won’t even get current version as they release the new OS, let alone recent inprovement