When Messages 3.7 rolled out a few days ago, something wasn't right with the app. On Android phones, Smart Reply was gone while other features were added, and on Wear OS watches, the app was crashing constantly. Thankfully, a new update to v3.7.052 on both phones and watches is rolling out, and it fixes both issues.
If you install the latest 3.7.052 Messages app on your phone, you may notice that Smart Reply is now back in the settings. You can toggle it on/off as you wish. If the feature doesn't appear for you, it may be behind a server-side switch and will show up later. On my Pixel 2 XL, it's back, though I can't test the feature as no one I know communicates over SMS - ha!
As for Wear OS, you simply need to update Messages on your watch and it will be fixed. The latest version loads up correctly and I can send new messages, view existing ones, and act on them.