Unable to update Apple Watch SE

I've got an Apple Watch SE I haven't used since Oct 2023. I wanted to use it again and luckily it charged, but obviously having not used the device for so long, its software is out of date.

It pairs to my phone easily via Bluetooth, but when I try to update the watch via the app on my phone- it shows me a buffering screen and it says "checking for update", and after a few minutes it says it can't connect to the watch (despite it being paired).

If I try to update via the watch itself, it tells me I need to accept T&C on my phone, but nothing appears. I can't use the watch app because it says "update required" and asks me to set up the watch, but I've obviously used it before.

If I try setting up the watch, I get the same notification that it can't connect to the watch. I'm trying to update my phone as of writing this, but I don't know how much of a change that'll make (updating from 18.5 to 18.6).

Is this a sign from god I shouldn't be working out? Starting to think it is.