It can easily be argued that Samsung's Tizen smartwatches are better than Wear OS competitors in a number of ways, but the voice assistant is not one of them. Bixby will never be able to compete with Google Assistant in this space, so it's always been a bit of a blow for Samsung watch owners. Until now, that is, as a new app is bringing the Assistant to the Galaxy Watch and others Tizen running 4.0 and above.
Developer Kamil Kierski is responsible for the app GAssist.Net which you can download from the Galaxy Store right now, plus the companion app for Android on the Play Store. The installation process may be a little bit complicated for some, but the pay off means it'll be worth it for many. You first need to generate a file from the Google Cloud Platform website and store it on your phone. This isn't as involved/scary as it might sound, and the dev has an explainer video on YouTube to help you through it. Once you've done that, make sure you have the Tizen and Android apps from above installed on your watch and phone, respectively.
You'll be asked to give some permissions on each, and then the apps themselves will walk you through the rest of the setup process. At this point, you should have a working Google Assistant on your Tizen watch. Unfortunately, you need to open the app an hit "Listen" for it to activate — there's no wake word functionality — but it's still good to have a capable voice assistant on your phone. According to some users on Reddit, it's faster to answer than the Assistant on Wear OS.
There will be certain things that don't quite work, especially controlling other apps (settings timers etc) on the watch and its hardware, but you can get personalized results working if you okay it for the device in the Google Assistant app on your phone (see here). It looks like the developer will continue to add new features where possible, too.