The tool Upscayl uses, RealESRGAN, is superior to waifu2x - waifu2x is really showing its age at this point. waifu2x is good if you want an upscale that basically retains the same level of fidelity while increasing the resolution (i.e., usually it’s blurry). Newer upscalers try to clean up the lines and make it look like it’s an original copy.
Edit: Just for fun, here’s some tests via downscaling a picture then re-upscaling it:
There are also other models available to test with beyond the stock RealESRGAN ones (I’m not sure if Upscayl can use them but they’re available for CLI use). I recommend using chaiNNer - e.g. you can use a setup like this