Zen is pretty much just the plain firefox hardening settings (check the privacy page on the e zen website). Librewolf and other hardened forks do a few more things than plain firefox (at the risk of breaking websites).

Of course even plain firefox is better than chrome, add ublock and a custom dns (nextdns or self hosted pihole/technitium) and you should be all good against most things.

Saying this as someone using zen with ublock and self hosted dns, so I might be biased 🙂

Some of the customisations librewolf does can be manually applied to ff/zen iirc

Lots of tracking can still be done.

Pick your poison for the situation, basically. If you really want to stop cross-site tracking for a browsing session, for example, use Cromite, which goes out of its way to actively spoof fingerprinting.

If you are really worried about surveillance for whatever reason, use a Mullad configs

If your ad profile is messed up, use an ad click spoofer instead of uBlock. If you’re concerned about security, use a browser inside a sandbox.

Zen with UBlock is just fine (I use it, sometimes), but there’s really no perfect solution. Keep a few browsers around, like tools for different situations.