I have a self hosted NC instance on the most current 26.x release. the builtin CODE server works fine in browser and on a second Android device not updated, and running 3.25. in the most current 3.26 as stated, there is no option for creating or editing other than for txt.
What happens when you try to open an existing Office document?
FYI: Using v3.26.0 without issue here, but not at my desk so unable to confirm against anything other than NC25.
Is a kown bug: