OnePlus smartphones are revered in XDA's community for their customizability and openness in software, but that doesn't mean that everything just works when it comes to custom ROMs. Developers still have a lot of work to do, and one feature that has proved difficult in particular with the OnePlus 6T has been the in-display fingerprint sensor. Until now, there were no public custom ROMs that could use it, though developers have worked in private Telegram groups with working builds for a while now. The Pixel Experience ROM has just been updated with a fully working in-display fingerprint scanner thanks to the work of XDA Recognised Developer vache, the developer of OmniROM.
At the moment, the Pixel Experience's ROM is in violation of XDA rules as the kernel source code isn't released, but the point is that custom ROMs with working in-display fingerprint scanners for the OnePlus 6T are coming. Vache says that his code is currently pretty buggy and messy, which is why it hasn't been implemented in OmniROM just yet. The main point is that the code exists on GitHub for other developers to take and modify so that it can be improved upon. This initial implementation may have bugs or be inefficient, but there's nothing stopping developers improving it in the future. These bugs include the fingerprint sensor not working in ambient mode or Always on Display mode. Not only that, using the fingerprint sensor breaks device panel modes after using.
Still, custom ROMs are coming with working in-display fingerprint scanners, though it's only a matter of time before they are perfected and work on the same level as OnePlus' implementation. Currently, users are required to use pin, password, or pattern to unlock your device, with some opting to enable Google's rather slow face unlock, as there are no other options for biometric unlocking. Previously, the fingerprint sensor was one of the biggest hurdles for developers to get over.