The decision was taken to change from a default of 128 kbps constant bit rate to a preset of 170-210 kbps variable bit rate. This was for those who wanted to export music for playing on their computer and could accept producing larger files in return for higher quality.
This does not suit all purposes, so to get what you were using before, change the radio button to “Constant” then in the “Quality” dropdown, choose a lower rate. You can also use “Variable” bit rate, but you can’t predict the exact size of the encoded file - it will depend on how hard or easy it is to encode the file.
The difference between “Variable” and “Constant” and “Fast” and “Standard” is explained in the Manual: MP3 Export Options.
If you want variable bit rate, use “Fast” unless there is some quality problem with doing so.