I don’t think wrong Collabora URL might result in slow Nextcloud but performance issues are known with integrated CODE. I would recommend you disable all involved apps using occ.
#check installed apps:
docker exec --user www-data {nextcloud-container} php occ app:list
#disable specific app (start with CODE and richdocuments)
docker exec --user www-data {nextcloud-container} php occ app:disable {app name}
once you have Nextcloud back to normal install/activate required apps one by one until you identify problematic app. In the past I had issues with external storage app which made Nextcloud almost unusable