Relief: kubuntu upgraded to 20.04 on laptop

[#1]

I have been shying away from upgrading my laptop from the 16.04 LTS for 2 1/2 years for fear of losing data. This despite doing regular backups.
Finally bit the bullet as 16.04 goes out of support this month.
The 'do-release-upgrade' to 18.04, then to 20.04 went smoothly, but it took ages for the machine to reboot each time.
Question:
I use kmail as my email client, and now the tab on the desktop panel has a number on it. Sometimes this relates to the number of unread mails in the inbox, but at others it is an apparently randomly incrementing number.
Does anyone know what this number really represents, and how do I configure it?

Regards,

Alistair

[#2]

Try asking here:-

https://www.linuxquestions.org/questions/linux-newbie-8/ 

(I'm not familiar with KDE).

[#3]

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@archerry wrote:

I have been shying away from upgrading my laptop from the 16.04 LTS for 2 1/2 years for fear of losing data. This despite doing regular backups.
Finally bit the bullet as 16.04 goes out of support this month.
The 'do-release-upgrade' to 18.04, then to 20.04 went smoothly, but it took ages for the machine to reboot each time.

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I had to smile at this as it brought back memories of my upgrade from 16.04 to 20.04 for a production server (low user count but important users never the less) and, getting somewhat bored during the update, I decided to fire up YouTube for some stupid reason... Evidently with the system in something of a half-upgraded hybrid state things like video deciding libraries might not behave too well and consequently the entire system locked up completely... There was no remedy but to pull the plug. Needless to say the system didn't boot afterwards and I had to enter into a self-taught crash course in how to get things back on track and enable the update to continue and, ultimately, complete. Surprisingly it did with just a bit of random mopping up to do afterwards. Lesson learnt there and next time I'll just go and make a cup of tea.

[#4]

@MJN 

There are only a few problems where cups of tea all-round does not help getting to a resolution.
One of first things I do on a new installation is comment out the "quiet splash" line in the grub file - I like to watch all the text scroll up the screen as it boots or shuts-down. No idea what much of it means, but it has helped once when a unit failed to boot. Linux User Group mailing lists are very useful.
A few years back, updates started to add the line back in several lines below the last active line - it took me ages to realise there was a new line below the bottom of visible text...
The release-upgrade does the same, so before rebooting after the second one to 20.04 I updated grub. Next time I will not, and will trust to any $deity(s) watching over me as it seemed to take even longer to reboot.
The teapot is calling...

Regards,
Alistair