I noticed two small bubbles on the carcass of my rear tire. I am running the 32mm Schwalbe Pro One tubeless at around 4bar /60psi and it wasn't particulary hot when the bubbles appeared (~20°C). The tires are quite new (~300 km) and I am completely clueless why the bubbles appeared. Has anyone seen this before and maybe has tips how to prevent it (or is it fixable)? Or is it just bad luck and a manufacturing fault?
This looks benign to me. The label patch clearly is a separate thin rubber layer put on top of the uniform sidewall, a cosmetic manufacturing detail. Until sidewalls seal, they usually leak minute amounts of air and sealant. What you noticed is probably a sidewall leak under the thin rubber layer. I'd pop it and let it seal by slushing sealant over it.
The image below shows the general structure of bike tires. It is from Vittoria's information page, but this generalizes across manufacturers.
@OshkoshBiker, in his answer above, alluded to the tire plies. A ply is a layer of fabric, usually nylon (older style tires used cotton!). Lamination in general is the process of manufacturing a composite material in multiple layers. Delamination occurs when the layers separate from each other. In the bike industry, the term is used in carbon fiber repair.
Basically, you should expect three carcass layers in a performance road tire. If they were delaminating, it should look pretty different from what you see above. If the top layer were bubbling up, it's one whole layer of fabric, so the bubble should not look thin. In contrast, if the photo you supplied is the only area where there is bubbling, then I have to agree with @Klaster_1 that this is much more likely to be just the label not adhering properly to the carcass.