After updating my Apple Watch to 7.6.1 the temperature no longer shows and I'm not able to add it back as a complication on my face. Also, the native Weather app is no longer installed. Is there a bug that needs to be fixed?

Here are the watch face types along with complications that should be available and customizable:

Apple Watch faces and their features - Apple Support

The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup just created. This should result in no loss of data. It deletes all temp and corrupted files and re-indexes the file system.

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

My watch will not display the weather eithet