Overlay for quick CYOA playing
You can also load them as straight .jpg or .png by changing H4QhXu5_d.webp to H4QhXu5.jpg or H4QhXu5.png. (Removing the _d, or it will be a thumbnail image.)
Er… What are you talking about in the first place? I don't recall adding any functionality related to modifying Imgur URLs anywhere. Or are you browsing mobile version of Imgur for some reason? Don't do that, it's crippled (intentionally so).
And if there's a legitimate issue when dealing with some galleries (on desktop site), please describe it properly (what you're doing, what you're expecting to happen and what you're seeing instead), and share a link to such a gallery so I can see the issue myself (and possibly fix it). The example you're giving me appears to have nothing to do with WebP (or galleries) in the first place, you're just trying to open a thumbnail instead of the actual image (and I don't recall encountering use of those except in actual thumbnails as well as in the crippled mobile Imgur version).
(To clarify: changing extension in URL doesn't actually affect image size at all. The thumbnail suffix, on the other hand…)
Imgur now uses webp for many images, which results in reduced quality because the expansion doesn't change the "maxwidth" in the URL.
Increasing it to an arbitrarily large number will improve image quality. For example:
https://i.imgur.com/H4QhXu5_d.webp?maxwidth=760&fidelity=grand
to
https://i.imgur.com/H4QhXu5_d.webp?maxwidth=1000000000&fidelity=grand