Cannot switch worksheet tabs when viewing .xls files

Expected behaviour

When viewing .xls Excel files with worksheet tabs I want to switch between the sheets.

Actual behaviour

Worksheet tabs are not selectable on view screen in Nextcloud app.
This problem inly occures with .xls files.
With .xlsx files I can switch between the sheets. It works as expected.
Note: When storing the .xls file to notes, I can open it inside notes and can select the worksheets. This is a workaround, but it exposes the data to Apple.

Steps to reproduce

Add .xls file including multiple worksheets to nextcloud server. Connect with app to server and open file. try to switch between worksheets.

Reasoning or why should it be changed/implemented?

This worked in earlier version and if Nextcloud App is able to show/render a Excel file it should provide basic functions to it.

iOS version

13.3.1

App version

2.25.6

Server configuration

Operating system:

Web server:

Database:

PHP version:

Nextcloud version: (see Nextcloud admin page)

Start by reproducing the issue in the iOS app with a multi-sheet .xls file, then compare worksheet-tab handling with an equivalent .xlsx file. Trace the file-viewing path implicated by the reproduction and verify that tabs can be selected for .xls files without changing the working .xlsx behavior.