Assuming you're set the template settings > catalog > Products display to "Switchable Grid"
You set the columns in /skin/reboot/js/reboot.js
You can adjust the col-x-x values
Code:
if ($('#body-container').hasClass('container-fluid')){ <----- Meaning the layout is set to full width
if (has_sidebar){
$list_cols = 'col-'+p_cols_mob+' col-sm-6 col-md-6 col-lg-6 col-xl-4 col-xxl-3';
} else {
$list_cols = 'col-'+p_cols_mob+' col-sm-6 col-md-6 col-lg-4 col-xl-3 col-xxl--5 col-xxxl--2';
}
} else {
if (has_sidebar){
$list_cols = 'col-'+p_cols_mob+' col-sm-6 col-md-6 col-lg-6 col-xl-4';
} else {
$list_cols = 'col-'+p_cols_mob+' col-sm-6 col-md-6 col-lg-4 col-xl-3';
}
}
If you've set the template settings > catalog > Products display to "Masonry"
You can change the columns by editing /skin/reboot/customer/main/products_t.tpl
Code:
{assign var="masonry_cols" value="col-12 col-sm-6 col-md-3 col-md-4 col-lg-4 col-xl-4"}
Info at
https://getbootstrap.com/docs/4.6/layout/grid/