Can't connect to NC after OS updates (maybe redis?)

I’m a little confused about your query - but it might be because I haven’t touched NCPi directly in a long time - but I thought updates were handled differently when using NextcloudPi (even for the OS and certainly for major NC dependencies like Redis).

NCPi is a bit of a special animal because even though it’s running on Raspberry Pi OS 10/11 and you can touch the OS directly still, it’s usually better not to because the pieces are designed to work together in a special way. There are a lot of assumptions made across the board. It’s essentially its own little sub-distribution of Raspberry Pi OS tuned specifically for running NC in a very specific way (or that’s what you end up with once you install it - particularly outside of Docker).

Are you saying you bypassed the NCP update process?

I.e. Staying up to date