Your new instance first needs to know about the community. You can nudge it into the right direction by opening Search, then type in !communityname@instancewherethecommunityishosted.com.
This might not return a result instantly - wait a few second, then search again and it should show up. From there others can find the community using a normal search, and once you (or someone else) subscribes to it, updates will be pushed to your new instance and it appears in ALL.
Keep in mind that this doesn‘t fetch older posts - you might not see any content in that specific community at first. It will however fill with new posts and comments from that point foward.
Won’t happen, not with the whole Hungary mess and the rise of the political far-right going on. No government would risk political suicide and the end of the Union for Sweden’s NATO membership.