Shipping textures as PNGs is suboptimal

This advice is only practical if you have proper import tooling that can transparently do this conversion for your engine and preserves import settings per asset. Otherwise, this just adds a ton of fragile manual steps to asset creation.

BS, Blender exports KTX2, your engine supports KTX2, Gimp exports DDS/KTX2, Substance Painter exports DDS/KTX2, three.js has a KTX2 converter.

Using image formats for texture formats is amateur game development. PNG’s are fine for icons or UI or while you’re still trying to figure out what you’re doing. Once you know, you switch to a faster, no translation required, texture formats that load faster, support physical layers, compression, and are already in BGRA format.

Note that KTX2 is a container format. It can contain uncompressed or compressed texture data. Some of the tools you mention might support "KTX2" but they won't compress textures for you, they just put the uncompressed data in a KTX2 container.

And my out-of-the-box Gimp 3.0.4. doesn't have KTX export at all. Didn't check the other tools you mention.