Vlad not OP, but I did some quick tests with duckduckgo, bing and google.
Both bing and Google have a character limit for their search box, so you can't enter more characters, for Google it is 2048 characters, for Bing it is 2000.
But when searching via the address bar (Firefox allows 5000 characters in the address bar for me), both search engines don't truncate the search query, at least it is not visible to the user.
DuckDuckGo does not have a limit implemented in the frontend, but it just gives you a "query too long" error popup after some threshold, and does not even execute the query.