This appears to be an issue with the responsive design (possibly intentional) of the Spotify site.
I tested this on both iPadOS and iOS; v16.6 on both devices.
- iPadOS loads the desktop site with no issues. The web player works without any problems.
- iOS will not load the desktop site.
- When no native (Spotify) iOS app is installed, the desktop site would fail to render or it would "glitch" while rendering
- When the native iOS app is installed, the site regardless of whether the mobile or desktop site was requested would immediately launch the application.
It's a moot point.
So the question is, whether there is any workaround!? Preferably with included support for uBlock Origin..
There seems to be an issue with the responsive design/user agent detection/scripting on the site. I opened the site in Microsoft Edge on a MacBook Air running Ventura; meaning that I was no longer using WebKit, but the Chromium engine. What I found was (using Developer Tools) that the website would render and function using a screen dimension that simulated a tablet (iPad), whereas it would crash/glitch when rendered as an iPhone.
The animation below shows the glitching I experienced on both my (physical) iPhone and the MS Edge browser dimensions simulating an iPhone. Keep in mind, this was on a desktop browser running on macOS 13.5.1 where the viewport dimensions was the only variable that was modified.

Bottom Line...
The web player is not going to work on an iPhone (likely not on Android either; not tested) due to how it renders with those dimensions regardless if your browser requests the desktop site or not. It will however render on iPadOS on both Safari and Edge; both having various AdBlock extensions available.