You are in the right place, and welcome.
The estate is quiet in this respect, but it does depend which version you go for.
From September 2018 the WLTP (new emissions cycle cars were introduced - copper SEAT
badge) - these have the gasoline particulate filter and no central resonator - therefore there is little you can do to improve the sound; even expensive full aftermarket exhaust systems do little to improve the acoustics.
Pre-September 2018, there was no gasoline particulate filter, and a removable central resonator that does improve the acoustics you desire.
There are a number of threads describing the differences of the ST300 pre/post WLTP. I guess it depends what you want.
For tuning: 'pre' has multiport injection, exhaust as above.
For spec: 'post' has improved digital dash, 7spd DSG.