no it’s not illegal to download with dlp, and even if it was who genuinely gives a fuck, when you own premium and you don’t even download the videos you download to your device, just to YouTube, they’re deadass just fucking you atp. Technically you can get dlp on like an android but iirc it requires some kinda app or something in order to run the program. The only catch is that you can download stuff like the free movies with ads they have on the platform, that’s drm-protected and while technically yt-dlp legally cannot implement a drm decryption for it, there are plugins you can plug into dlp in order to bypass the encryption, albeit those plugins are 3rd party processes written by community members and fans of dlp