Just thinking about the position of some console companies is rooted on closed eviroments and exclusives like, for example, if nintendo published their games on other platforms probably steam deck would replace it right away (IMO) do you think it would also affect companies like play station or xbox?
I believe it would do the exact opposite. Exclusivity is the opposite of competition. A company monopolizes content by only allowing it to be hosted on its own platform. In a sense, yes, Nintendo holds a monopoly on Mario games, Zelda games, etc. If there were no such thing as a console-exclusive game, other console makers and especially Nintendo would be forced to compete in other ways should they want to continue existing. This could mean making competing hardware (eg. better value, better features, more powerful, etc), making a better storefront, and of course, making better games.
Also, it’s worth mentioning that despite having a far, far larger library of games, the Deck is still an extremely niche system, and definitely not the market-destroying monster that many here wish it is. The Switch has sold over 40 times more units than the Deck if we’re being generous to Valve. Even the PS Vita, widely regarded as a failure of a handheld, sold 5 times more units than the Deck. Nintendo and Sony are much more familiar household names than Valve, and they market themselves far more aggressively. Should Nintendo release another handheld while also forgoing any exclusive games, I guarantee that it would still sell far better than the Deck.