That actually makes a lot of sense, the skills that built a loyal following in the C64 scene are really different from what modern platform discovery needs, it's not that your marketing instincts are off, it's just a completely different landscape with its own rules.
This is genuinely my area of expertise though, I specialize in exactly this gap, taking games with real quality behind them and building visibility on modern platforms through short-form video content and consistent social presence. For something like Vault of Seraphim XL, I'd focus on turning gameplay moments (the new controller support, fullscreen, whatever feels satisfying to watch) into short clips that get it in front of players who are actively looking for platformers like yours, people who'd probably love it but just don't know it exists yet.
If you're open to it, I'd be happy to put together a few specific ideas tailored to the XL games and walk you through how that could look, just want to help you get the same kind of traction on modern platforms that you've already built in the C64 space.