GG.Deals doesn't offer an export function, and Backloggd has it on their public roadmap. In the meantime, you can try importing a text list.
Import from GOG
GOG has no public API, so we're going to read the same endpoint their own site does.
That list also covers DLC and extras, and those mostly won't match, so expect a few misses.
That list also covers DLC and extras, and those mostly won't match, so expect a few misses.