The OnePlus 5 and OnePlus 5T can be upgraded to Android 11
The OnePlus 5 and OnePlus 5T have received better software support than most Android smartphones, but neither are ever likely to receive Android 11 officially. OnePlus has acknowledged that official support has dried up since the release of Android 10 to the devices too, but at least the OnePlus 5T should receive one or two more security patch updates. OnePlus 5 and OnePlus 5T community development remains alive and well though as the two devices have just received their initial Android 11 ROMs.
The Yet another AOSP project (YAAP) is currently in alpha, so things like SafetyNet and the Alert Slider are broken. However, most other features are working, including the camera, fingerprint scanner, DASH charging, DRM and Wi-Fi. YAAP has GApps pre-installed, along with 'some pixel additions'. The initial build contains a newer set of Android security patches than the most-recent OxygenOS builds, too.
Early adopters of YAAP have reported that the initial build runs smoothly, despite it being in alpha. Apparently, even dirty flashing the ROM does not result in any major bugs. YAAP is available for both the OnePlus 5 and OnePlus 5T, but ArrowOS has also been ported to the OnePlus 5. Another AOSP ROM, ArrowOS has fewer issues than YAAP. However, it is worth noting that encryption does not work and SELinux is set to permissive.