I tried comparing this image with some from the Hubble and this one appears to be slightly sharper (not to mention much more detailed in terms of the atmosphere thanks to the infrared wavelengths). I don't think it gets too much higher-res than this without a probe getting close to the planet.
A google search indicates Neptune's largest apparent size in the sky is 2.4 arcseconds[0], and a commentor below suggests JWST's resolution is approximately 0.1 arcseconds (.068 at a wavelength of two microns[1], from some google searching), which would suggest a rough maximum resolution of about 35 pixels, while this image is 80. I'm unclear on the exact reasons for this difference.
A google search indicates Neptune's largest apparent size in the sky is 2.4 arcseconds[0], and a commentor below suggests JWST's resolution is approximately 0.1 arcseconds (.068 at a wavelength of two microns[1], from some google searching), which would suggest a rough maximum resolution of about 35 pixels, while this image is 80. I'm unclear on the exact reasons for this difference.
[0] https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact....
[1] https://www.stsci.edu/files/live/sites/www/files/home/jwst/a...