Memcached and redis are installed and running? why doesn't nextcloud see them?

If Redis is already used by Wordpress, for example, then you have to make sure that they don’t get in each other’s way, so you should put Nextcloud on a different database. By default the used database is with index ‘0’ but you can also go to ‘1’ or ‘2’ or whatever index.
The number of databases that Redis provides is set in /etc/redis/redis.conf with the variable databases

Thats a complete different issue.

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