Does only Universe 7 (& 6) have Dragon Balls?

[Shorty GZ2]

Probably obvious that it's because there are Namekians in those universes (plus Zalama in U7 for the Super Dragon Balls), but it's known now that they aren't native to them & are instead from the Demon Realm, which spans across all universes as of Daima

Since it seems the concept/existence/use of the DBs themselves aren't a well-known fact even in U7 (Bulma says the last one who found all 7 before her centuries ago wished to be a king), could it be possible that there are Namekians & DBs in other universes that just haven't been found/used up until now?

[Omori]

With the creation of the multiverse and Namekians having left the Demon Realm, it's certainly possible that some groups went to other universes. Maybe even much earlier than the ones who came to U7 (and possibly U6).
But possibly lesser known as you mentioned. Could be something interesting for future stories.