I don’t know what to tell you, but just because people are selling GIFs and memes doesn’t mean you’re legally allowed to sell whatever samples are lying around on your computer. Copyright laws exist, and unless you have permission to sell something you can’t legally sell it.
Here’s another example (from Image-Line’s support) - you’re not allowed to sell anything derived from FL Studio’s demo songs. If you do that you’re violating copyright.
This is also true of basically all the sample libraries. In this case I checked all the Kontakt instruments and Spitfire libraries I have, and they all prohibit selling derivative non-musical work. This means you are allowed to sell music tracks you create, but you are explicitly prohibited from resampling, remixing and modifying the samples and selling those individually or as part of a VST instrument or a sample pack.
Here’s an excerpt from Spitfire’s EULA
This license expressly forbids resale or other distribution of the Products or their derivatives, either as they exist in the library, reformatted for use in another sampler, or mixed, combined, filtered, re-synthesised or otherwise edited, for use as sounds, multi-sounds, samples, multi-samples, sound sets, programmes or patches in a sampler, microchip, computer or any sample playback device
It’s also worth noting that some (i.e. Spectrasonics/Omnisphere) actually prohibit you from distributing stems of your music and only allow you to sell mixed tracks with more than 1 instrument. Yes it is dumb, but that is what their license says.
Of course there’s the question of “do I get caught?”, but with how advanced digital printing is getting (and AI), personally I’m extremely wary of doing anything illegal w.r.t. selling samples, because it could very well end up being automatically picked up by a bot that scans for said fingerprints in all sounds uploaded to libraries where you sell them.
In general, based on what I’ve found so far it seems that anything that relates to samples in any way (including i.e. sample oscillators in Pigments) is generally prohibited to process/re-sell in any way, and synths in general only prohibit sampling their builtin presets as they’re copyright protected. Since the Digitone only has presets and no builtin samples, my question was mostly about those.
edit: One more important addition. Keep in mind I’m not a lawyer and I could be wrong, but imo caution is always good with these things. The license of the instrument is one thing, but services for selling tracks (i.e. audiojungle or pond5) often explicitly prohibit certain things too. So while your Kontakt instrument might allow you to create SFX for games and sell those, the site where you want to sell them might explicitly prohibit selling samples which aren’t your original work.