We are happy to read these interesting and useful informations in the community ;-)
If you want to cross post, you hit the 3 little dots under the post and select cross-post, then the post will be shared in the community but you won't get any reward, as far as I know,
Rewards are automatically declined for the cross post and discussions under cross post will be different and will follow different community guidelines.
so my advice is to post first in the right community, where interested-in-the-subject-people will read and upvote your post, and only after cross-post it elsewhere.....
Of course you are not always aware of all the communities available, but you can always cross-post an old post of yours, and as written above, the rewards will be declined ;-)
Hope that helps