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I don't mind just putting it like this, it's okay, I feel like it's too early to pay attention to sound insulation, thermal insulation or something, just find a master who makes aluminum alloy doors and windows to change it for you.
The one you said is called a toilet seat, you can replace it with a new one, there are sales on the Internet, you can replace it.
It should also be possible to glue, but if you do waterproofing, you can make the area larger and more reliable.
Use a detergent (available in supermarkets) that specializes in washing tiles! Scrubbing with hot water is more effective!
Use a wallpaper knife to scrape the glass glue clean, press the new toilet, and use the glass glue to glue along the toilet bowl for a week, and it can be used normally after 12 hours.