Official LineageOS 20 was released today with support for the Pixel 5. As such the next release of Wunderment for the Pixel 5 will be based on 20. Also, the all of the OnePlus 5 through 9 devices have LineageOS 20 support, and The 5T and 6/6T will be migrated to LineageOS 20 as well.
The OnePlus 7/7T/8T/9 will remain on LineageOS 18 as this is the last version that supports bootloader relocking for these devices. LineageOS 18 is feature frozen at this point, but support will continue at this time.
Support for the Pixel 6/7 on LineageOS 20 has not yet been officially announced, but once it has been the 6 will be added to the officially supported WundermentOS builds, with the 7 following at some point in the future once a build device is available for testing./.
WundermentOS 20 has already been in beta testing and so far has been stable, so no issues are expected to be had during the upgrade between major versions.