The LineageOS custom ROM is best known for its wide range of device support. In the past month alone, the project has added the Razer Phone, Zenfone 6, and other phones to the official roster. It seems a bit strange that they weren't already available, but ports for the OnePlus 6T and 7 Pro are now live.
LineageOS has now added support for the OnePlus 6T (code-named fajita) and 7 Pro (guacamole), thanks to the work of maintainers LuK1337, PeterCxy, and Tortel. Both devices are receiving daily builds based on LineageOS 16 (Android 9 Pie). Since these are officially-sanctioned releases, there shouldn't be any breaking bugs.
It's always great to see Lineage add more flagship phones to its roster, as the current selection is somewhat lacking if you don't have access to Xiaomi devices. The more the merrier!