There is not a single day goes by where I see something like this dialog in Ubuntu Software Center

For diagnostic purposes, what output do you receive for the commands (to be executed in a terminal window):

uname -a
lsb_release -crid
timedatectl
sudo apt update

pranav@Inspi5548:~$ uname -a
Linux Inspi5548 5.0.0-25-generic #26-Ubuntu SMP Thu Aug 1 12:04:58 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
pranav@Inspi5548:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 19.04
Release: 19.04
Codename: disco
pranav@Inspi5548:~$ timedatectl
               Local time: Wed 2019-08-21 23:24:08 +0545
           Universal time: Wed 2019-08-21 17:39:08 UTC
                 RTC time: Wed 2019-08-21 17:39:08
                Time zone: Asia/Kathmandu (+0545, +0545)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no
pranav@Inspi5548:~$ sudo apt update
[sudo] password for pranav:
Hit:1 http://archive.ubuntu.com/ubuntu disco InRelease
Get:2 http://archive.ubuntu.com/ubuntu disco-updates InRelease [97.5 kB]
Get:3 http://archive.ubuntu.com/ubuntu disco-backports InRelease [88.8 kB]
Get:4 http://archive.ubuntu.com/ubuntu disco-security InRelease [97.5 kB]
Get:5 http://archive.ubuntu.com/ubuntu disco-updates/main amd64 Packages [248 kB]
Get:6 http://archive.ubuntu.com/ubuntu disco-updates/main i386 Packages [211 kB]
Get:7 http://archive.ubuntu.com/ubuntu disco-updates/main amd64 DEP-11 Metadata [131 kB]
Get:8 http://archive.ubuntu.com/ubuntu disco-updates/main DEP-11 48x48 Icons [15.2 kB]
Get:9 http://archive.ubuntu.com/ubuntu disco-updates/main DEP-11 64x64 Icons [38.2 kB]
Get:10 http://archive.ubuntu.com/ubuntu disco-updates/universe amd64 DEP-11 Metadata [62.1 kB]
Get:11 http://archive.ubuntu.com/ubuntu disco-updates/universe DEP-11 48x48 Icons [32.6 kB]
Get:12 http://archive.ubuntu.com/ubuntu disco-updates/universe DEP-11 64x64 Icons [96.1 kB]
Get:13 http://archive.ubuntu.com/ubuntu disco-backports/universe amd64 DEP-11 Metadata [7,920 B]
Get:14 http://archive.ubuntu.com/ubuntu disco-security/main amd64 DEP-11 Metadata [33.8 kB]
Get:15 http://archive.ubuntu.com/ubuntu disco-security/main DEP-11 48x48 Icons [8,745 B]
Get:16 http://archive.ubuntu.com/ubuntu disco-security/main DEP-11 64x64 Icons [21.4 kB]
Get:17 http://archive.ubuntu.com/ubuntu disco-security/universe amd64 DEP-11 Metadata [17.5 kB]
Get:18 http://archive.ubuntu.com/ubuntu disco-security/universe DEP-11 48x48 Icons [14.3 kB]
Get:19 http://archive.ubuntu.com/ubuntu disco-security/universe DEP-11 64x64 Icons [44.7 kB]
Ign:20 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:21 http://dl.google.com/linux/chrome/deb stable Release
Hit:23 http://ppa.launchpad.net/git-core/ppa/ubuntu disco InRelease
Get:24 https://packages.microsoft.com/repos/vscode stable InRelease [3,182 B]
Hit:25 http://ppa.launchpad.net/libreoffice/ppa/ubuntu disco InRelease
Get:26 https://packages.microsoft.com/repos/vscode stable/main amd64 Packages [134 kB]
Hit:27 http://repo.mysql.com/apt/ubuntu disco InRelease
Hit:28 http://ppa.launchpad.net/lyzardking/ubuntu-make/ubuntu disco InRelease
Hit:29 https://repo.windscribe.com/ubuntu bionic InRelease
Hit:30 http://ppa.launchpad.net/qbittorrent-team/qbittorrent-stable/ubuntu disco InRelease
Hit:31 http://ppa.launchpad.net/teejee2008/ppa/ubuntu disco InRelease
Fetched 1,404 kB in 14s (98.9 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
pranav@Inspi5548:~$

I barely use "Ubuntu software" for the update.
I do all the updates from the terminal.

But whenever I visit Ubuntu Software, it annoys me a lot by showing me these pop-up messages again and again.

As if it's asking me to not use Ubuntu Software, like never.

Sorry, no idea what the root cause might be.

Me too.

(Expected something more from u, but I guess this is it.)

The error message shown on imgur.com is

Unable to download updates:
failed to refresh cache: E:http://archive.ubuntu.com/ubuntu disco InRelease is not (yet) available (Temporary failure resolving 'archive.ubuntu.com')

The error message refers to the central repository server. You might consider switching to a different one, either the country server for your country, or a local server in your vicinity.