It violates the spirit of what you probably want, but there are some amazing free upscaling options these days.

I recently found a pic from behind-the-scenes of an old favorite movie of mine. It was exactly the kind of photo I wanted, but woefully small. With minimal effort and Real-ESRGAN (and perhaps a touch of artificial film grain), I blew it up to a very crisp B&W poster I framed. I'm still looking for errors in it.