The manager goes ahead and add it to the backlog and no credit is given. Easy peasy.
(the second part may not happen publicly or immediately, rather, the project would seem to be dismissed or postponed)
There also nothing wrong with self-promotion and singing your own praise. So when discussing with others you might say something like "I got this idea and discussed with Mr Manager who liked it and added it to backlog".
At the end of the day if he does take credit and no one knows… the bright side is you had a good idea, go somewhere else where they will recognise you for it.
It's helpful to differentiate between the two - ideas aren't really worth much, but credit where its due can be important.
Equally, if you are newish to a place you'll have lots of ideas. Some of those ideas will be new, and useful. Some will be old (tried and failed) some will be old (never got high enough on the priority list.)
Perhaps the biggest disconnect though is that while your idea may be objectively good, it may not serve the goals of the organization. This can be hard to understand if you don't know the organization well.
For example, faster reports are a good thing, but 5% faster at the cost of maintainability is good in the short term, but bad in the long term.
Or you may be an expert in say Haskall, and can quickly whip up some utilities in Haskall, but your manager wants it in VB# because that's what everything else is written in, and he's concerned about life-after-you.
Lastly, and thus is going to sound harsh, but there's not a lot of "credit" for good ideas in the first place. Ultimately nobody cares who -thought- of it, they really care who -did- it (and that includes sales, management etc.)
A common refrain about startups is that ideas don't matter but execution does. If you work at the same company, how is it idea theft? What expectations do you have with credit for an idea? bigger bonus? promotion?
Execution is the sauce.
If you are proposing ideas, have a working MVP to demonstrate this.
I’m curious what that would be? Why do you believe your org would do it?
Some orgs reward ingenuity. Many do not.