There’s now a dedicated repository hosting XLibre third-party packages for Manjaro at https://xlibre-manjaro.github.io. The packages are built utilizing the official Manjaro build Docker image. This should isolate them from any upstream Arch changes not available on Manjaro yet.
We at XLibre are currently also consolidating the whole Arch packaging process and its primary mirror on https://xlibre.net at Index of /repo/arch_based/x86_64/. There’s a good chance we’ll be able to host the Manjaro-specific packages there as well.
I’d kindly invite you to test the solution and report any issues you encounter at Issues · xlibre-manjaro/xlibre-manjaro · GitHub. I did so myself using XLibre with the modesetting driver, and it worked.
We’ll officially announce the XLibre for Manjaro third-party package repository after some time of testing.