I need Gutenberg doesn’t mess with my HTML

I understand it’s the future, I use it on most of my articles but I sometimes I need to add some specific HTML code and I need Gutenberg doesn’t mess it up!

Every time I save and reload I find some quotation marks are changed (often from single ones to double ones) and this spoils all the code. Sometimes I find a block is invalid (most of times because Gutenberg has changed something like quotation marks).

It’s impossible to have a website working if Gutenberg keeps doing intrusive changes! I need some HTML code with its own classes, I need specific characters ins specific places. The old classic editor didn’t change anything and everything worked.

Please, help me. If Gutenberg blocks can’t ignore my code, is there any other custom block that can do that? I need that everything I write in a block stays exactly in that way, even if Gutenberg thinks it’s wrong.

Thanks.