I've never tried this, but if what people say in this thread about how PETG doesn't bond well to PLA,
Then you'll definitely need to adjust your Z-Interface distance between support and bottom layers. The default is likely too much of a distance.
I don't know what your slicer setting is called, but in PrusaSlicer its called "Top Contact Z Distance" in the support settings, and when it comes to PLA vs PLA, it has an extra 0.17mm distance added.
If I were you, I would try 0.05 or even none.
Fixed that for you,
There are far more bots that you realize.
Fake upvotes and fake comments, to drive the few people still on there to keep providing content for free.