These are the key bits:
"Exception":"RedisException","Message":"No such file or directory"
"Exception thrown: RedisException",[...],"version":"30.0.2.2","exception":{"Exception":"RedisException","Message":"Redis server went away",
Some ideas / things to check
Is your Redis service actually running?
Does /var/run/redis/redis.sock exist?
What are the the ownership and permissions for the UNIX socket (file) /var/www/run/redis.sock?
Review the steps again, in case something minor was accidentally overlooked, in the caching section of that tutorial you are using (Note: I did not review the third-party tutorial in any way).
Do my system logs have any Redis related entries? (e.g. journalctl -ar and/or contents of /var/log/)?
Cross-reference what you have setup already with another tutorial such as this one which was recently posted on this forum.
Maybe try switching Redis to TCP (be careful: don’t bind it to a public IP address) and adjusting the Nextcloud config to use it at that IP:port combination. If that works, you can decide whether to leave it like that or try to reverse things step-by-step until you uncover the underlying problem from your original attempt.