LineageOS hasn’t been heard of for a long time, but the successor to the CyanogenMod is far from dead.
Not much has happened in the Android modding community for years. There is almost no need for modified software anymore, manufacturers’ omissions are much less severe today. The demand for custom ROMs has collapsed. That’s why it was recently foreseeable that even larger projects like LineageOS could only barely survive. If previously there were multiple news items to report at more regular intervals, it has recently gone silent.
LineageOS with Android 10 will continue to exist
A look at the LineageOS blog shows this. There hasn’t been a new changelog update since July. However, the work continues in the background and there are new versions for the supported devices so far. A look at Reddit also shows that LineageOS is not completely dead yet. However, many employees are inactive. Just not someone who had good news in a subordinate clause.
A user asked about a feature that was no longer available in Android 9, to which the LineageOS administrator replied that said feature would return with Android 10. So hopefully with LineageOS 17, I take it from this answer. But this is unlikely to happen before the spring of next year.