How to open PDF files on Telegram with my preferred application in Kubuntu?

Whenever I open a PDF document in Telegram, it opens in Xournal++. But I want it to open with Okular, which I have set as the default PDF reader.

PDF documents in Dolphin do open with Okular. How to make PDF files in Telegram open with Okular?

I am using Kubuntu 20.04, and the binary executable for Telegram.

KDE settings does not have any entry for default PDF application. Dolphin has settings to set a default PDF application, but that probably only applies to Dolphin.

Solution 1:

I had the same problem. After read this link I've tried to change the order of applications in kde PDF file properties then saved. After that I've restored Okular as primary handler and saved. Finally I've quit and restart Telegram and it started to open PDF with Okular.

Solution 2:

Try setting the default application back to Xournal++ and then switch back to okular. This apparently solves the problem in some cases.