They didn't have much choice, unfortunately: https://community.signalusers.org/t/signal-blog-removing-sms...
Google has not provided any public API for RCS, and they control the ecosystem fully. If Google wanted other clients to use RCS as a platform, there would be public APIs that Signal, iMessage, Textra, Facebook Messenger and other SMS clients could integrate with.
Actually, there is an RCS API.
However, Google restricts its use to themselves and specific OEMS only. IIUC, that's currently only Samsung[0].
[0] https://www.xda-developers.com/google-messages-rcs-api-third...
IIUC, the RCS API is not part of AOSP[0], and as such, not part of LineageOS. As such, I believe the answer is "no."