Hi Stoyan and thank you for your reply.
The problem is that the siteground-optimiser-combined-css is not controlled by me. It’s a plugin that is doing one specific task and it seems that is not optimised as it should.
This website is not heavy or including hundreds of photos, so to include so many unused bytes, it only shows that the plugin is misbehaving.
Also, to reduce the CSS that is causing the issue for the siteground-optimiser-combined-css is something that is not clear.
How could I know which CSS is the culprit?