Why my cursor is changing when I move?

[Rinate]

I have changed one with Tweaker. Alright, my cursor was changed, but when I move for example: from browser -> telegram, the cursor changes. And one more question, why "Ubuntu Software" does not have texture with any themes expect default?

 

[Alexzee]

If you'd like to have more themes install Gnome Tweaks.

How to Change Theme on Ubuntu 18.04 LTS & Above - OMG! Ubuntu

Learn how to change theme in Ubuntu quickly and easily, without terminal commands or odd apps. In fact, you already have everything you need to do it.

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To answer your question:
Depending on what desktop envirnment Ubuntu is using there may not be any other themes to choose from.