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No, SharePoint Modern site does not have concept of master page. Hence you won't able to directly customize as we used to do in classic experience. You can customize modern site using below options
Create Application customizer to add header and footer on page.
You can create modern custom pages and select layout like one column, 2 column etc...
You might ...
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I am afraid, top suite bar cannot be controlled from master page. It is being rendered directly from content database. If you want to hide settings gear icon for non- SharePoint admins users you have to do it via custom javascript code.
You need to add javascript code on document.ready
What we would do is use default page context info attribute ...
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You'd need to create copy of the seattle.master and modify and use that as master page. SharePoint doesn't allow modifying the seattle.master as it generates it from the seattle.html.
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