I found some examples for working/non-working websites, yandex Russian is detected and offers a translated version, but niconico Japanese isn't detected, I am not sure what differences are important.

Do you mean imageSource is nil inside the function or when you change the return type to a CGImageSource? and return the value? The image file type, is it really supported by macOS?

launchd tells 49187: (os/unix) operation on device would block Maybe an update has mounted/booted from an APFS snapshot? If you have a 128GB internal disk it can be especially difficult to make enough free space to satisfy Boot Camp Assistant unless you do an erase and install.

Number of charging sessions, charging rate and more generally speaking temperature could affect the reported battery health. For example charging 10 times a day and keeping your phone at 95% - 100% would wear out the battery faster than if you charged from 50% up to 100% once a day. If your iPhone supports fast charging and you use a Mac or USB-PD charger it could shorten charging time and at the same time decrease battery health faster. Disabling optimized battery charging might magnify these effects. Just taking the numbers from the 20% decrease over 500 charge cycles yardstick (which I think is used for warranty repair determination) at 30 days × 50% = 15 charge cycles, you might interpolate and expect 0.6%, but that rounds to 1%, and your 2% might be rounded up from 1.5%. Your iPhone probably didn't leave the factory 1 month ago, and if you've only ever discharged your phone to 50% then there's the possibility that the estimated "battery health" percentage comes with a wider margin of error. i.e. There's little use speculating over an iPhone estimating 98% battery health if it performs as expected.

You don't need a developer certificate if you're just going to test and run on your machine, but you need to "Allow Unsigned Extensions" under the develop menu. I'm not entirely sure but I think the safari extension "wrapper", actual web extension files and the containing app still need to be ad-hoc signed in this case.