occ is the main tool for administration on Nextcloud on the server side, you can manage almost anything from it included nextant.
It’s placed on your nextcloud installation directory and is used along with php, so you should run it like
sudo -u www-data php occ your_commands,arguments and paths here
(if you run debian based system)
I’m not familiar with linuxserver docker image, but you might wanna enter that image and run the occ commands within the docker image (it doesn’t matter that Solr is running on your machine).
Finally you might wanna follow/support the FullNextSearch development since that will be the next step on this matter.