Apple is fully testing a prototype of the 2021 iPhone, and according to a Bloomberg report, it has a fingerprint reader under the screen.
Rather than being a replacement for Face ID, this would be an additional method of unlocking the iPhone. Alternatively the passcode could be used.
However, according to the report, it is still not decided whether Touch ID will return in this year's iPhone models. (There are various patents for under-screen Touch ID).
The report also mentions that Apple is discussing removing the Lightning port on at least some iPhone models this autumn, and instead relying entirely on wireless charging. As above, this strategy has not yet been decided upon. (Apple has filed for a patent to improve the Lightning cable, so that does suggest that it won't be cutting it out quite yet, read: Apple patents fix for fraying Lightning cables)
Bloomberg also indicates that the iPhone 13 will be a minor update - as previously stated. According to Bloomberg, this is be considered an "S-upgrade", i.e. a year with slightly less news.
The report also indicates that Apple is doing some early work on a foldable phone, although we are unlikely to see this before 2022.
Analyst Ming Chi Kuo published investor guidance around the time that the Bloomberg report came out in which he said that high-end 2021 iPhones will use a "vapour chamber thermal system", via Apple Insider.
Apparently this thermal system is a necessity for the upcoming high-end iPhones to match their stronger computing power and faster 5G. This system is being "aggressively" tested by Apple.
The vapor chamber cooling technology is designed to keep a device cooler when it is under heavy stress. Kuo anticipates that Apple will have high requirements for this technology, but he expects the high-end models will adopt it. Smartphones from Samsung, Razer, and LG already use the vapour chamber thermal system.
Find out everything we know about the iPhone 13 (or iPhone 12s) in our 2021 iPhone hub.