Have you seen the LanguageMaster extension? We do LingQ overlays on video players (YouTube/Netflix/Disney+/Amazon Prime etc…)
Anyone who purchased the MasterLingQ extension before November 2024 is eligible for a lifetime account.
Another user @vet8t6z79pc4 seems to have put a large amount of time and effort into improving the YouTube player experience on the LingQ website. His solution is free but is asking for a donation if possible.
Regarding the adding of single words/phrases without importing a lesson it is very doable. A dummy lesson would be setup and then additional words / phrases can be added on demand.
It is also unlikely to get a response from LingQ devs here without directly tagging them or posting in the support forum.