or is it that i am missing on a important source?

Have you tried this

Execute the command: mousepad /etc/apt/sources.list
Remove everything within that sources.list file
Duckduckgo for "Kali Linux Repository" (https://docs.kali.org/general-use/kali-linux-sources-list-repositories)
Scroll down and look for "The kali-rolling repository"
Copy everything within that kali-rolling and paste on sources.list file
Save the sources.list file
Execute the command: apt-get update
Now install your package(e.g:apt-get install tilix)

Or perhaps try

wget https://github.com/gnunn1/tilix/releases/download/1.9.3/tilix.zip
sudo unzip tilix.zip -d /
sudo glib-compile-schemas /usr/share/glib-2.0/schemas/

Because you might have to install it manually because Kali are normally a few versions behind on most tool repositories so.

Tried renewing sources many times. Same issue. Usually Tilix can get easily installed on kali linux. I installed kali newly again on vm using week 45 installer iso file. I had this problem so I recreated my sources.list many times. Same issue.

Yeah I was able to install tillix by normal manual method but it was unnecessary.

Are you able to install Tilix?

Unfortunately, it was removed from Debian testing (which Kali is built on) - https://tracker.debian.org/news/1180947/tilix-removed-from-testing/ which also caused it to be removed from Kali.

@dQw4w9WgXcQ I appreciate that you are trying to help but please refrain from doing broad assertions when you are not sure.

Because you might have to install it manually because Kali are normally a few versions behind on most tool repositories so.

This is just plain wrong. It's quite the opposite, Kali is based on Debian testing which gets the lastest updates when the package is well maintained in Debian. In the case of tilix, the package has been dropped from testing due to a bug that has not been handled by its maintainers: https://bugs.debian.org/968816
See https://tracker.debian.org/pkg/tilix for more information about the package in Debian.

So you should really get in contact with the Debian maintainer and/or offer your help to get the package fixed in Debian and then it will come back to Kali.

I sent a short mail to the Debian maintainers to make them aware of the package removal, hopefully that will trigger some action.

I apologise because English is not first language and sometimes I might have misunderstanding at some things.w

Sorry if I offended or upset you any way.

Ok I got it. For now I have manually installed Tilix by the instructions provided in their GitHub page and the same are also provided above in this thread. I hope after Tilix is brought back to debian everything stays fine and nothing breaks because I have manually installed Tilix