How to delete/hide the button in category

Here is a simple CSS trick.

1. You can right-click on the button -> 'Inspect'
   
2. In 'Elements' tab, see the button element. Check what class is it using
   
3. Goto Customize and put CSS code to hide the button

/* Code for hiding button*/
.class-name {
display: none!important;
}

Change the 'class-name' with your own class name.

I spun up a site with that theme and took a look at that button.

It doesn't look to have a very specific class or ID assigned to it, so your best bet would be to make sure to include Category as a part of your CSS, so it's specific to the category archive page:

.archive.category i.fas.fa-layer-group{
display: none !important;
}