forget Realergsan - classical is the best

upscaler rename it to *.pth and copy into \ESRGAN or \RealESRGAN or upscaler path

orginal link:

https://openmodeldb.info/models/2x-classicalSR-DF2K-s64w8-SwinIR-M

also this is worth a try:
https://huggingface.co/Phips/4xRealWebPhoto_v4_dat2/tree/main

and thats very good for faces (8x_NMKD-Faces_160000_G)

https://huggingface.co/datasets/mpiquero/Upscalers/tree/main

but if you want real nice upscale... best for 700pix and lower -> use topaz gigapixel ;)