Do you have examples? I use Safari and don’t find this to be true. Given Safari is what people use in iOS, id expect this to be rarely the case (most sites will test on an iPhone).
Same here; I don't know if I've ever seen a site that works in Chrome but not Safari (I don't doubt they exist, I just don't tend to come across them).
As a MacOS Safari 12 user, I've recently come across several important sites where some functionality fails hard in Safari yet works in Chrome ie barclays.co.uk and easyjet.com
I don't have any proof but my suspicion is that I've seen more sites failing Safari since Mojave.
I really dislike (& distrust!) using Chrome now, especially for e-commerce sites or anything with SMS based 2FA as Safari's ability to pull codes automatically from messages is a godsend.
I created an internal application for our company to use that is essentially a directory of staff members. I do most my development in Chrome but the bulk of the users are on iOS (Safari). I always find little nuances that I need to tweak for things to be "just right" on Safari. One example is that in all other browsers (including Safari Desktop) a <input type="search"> will show a little clear button ("X") at the end of the input. Some bug removed it from iOS Safari and we're still waiting for them to resolve the issue. It was reported in 2016 and was acknowledged by Apple [1]...
Chrome also frequently attempts to cover up incorrect code with what it thinks the author probably meant. Firefox tends to be much better than Chrome at following the actual spec.
I tend to develop primarily with Chrome first for some different reasons (ability to disable CORS, support for self-signed certs with WebSockets, and its better debugging of WS frames), but I always make sure to test later with Firefox and Safari, and occasionally find code that worked in Chrome, but doesn't elsewhere, and the reason is almost invariably always that Chrome didn't follow the spec.
Fair enough about it not being in the spec. It does appear to be a part of Apples' "Human Interface Guidelines"[1], although these guidelines are pointed to native applications. It was just an unexpected regression that occurred during the rollout of iOS9 and is an example of one of the little nuances that caused me to do something different. I've had some other issues regarding scrolling and focus, but this one seemed to be easier to talk about.
I have seen this many times during development. Noteworthy sites that cause problems are, well, Microsoft sites: portal.azure.com - problems downloading publish profiles.
SharePoint - too many to mention
Cant come up with example but i have fixed quite a few safari issues as a web dev. Often they dont appear on iphones because the media queries for mobile are tested on iphones, but desktop layouts are tested on chrome. Safari had a few flexbox quirks that caught me out most recently.
