It depends on your use case. As you can create Public Board. In Board you can create shareable view where your client can see their data only. Same goes for client B. They both won’t be able to see each other boards.
But if you want them on communicate as well, then you need to create private board and invite them for collaboration.
If you need furthur assistance please do not hesistate to DM me.
Rehan AQ | Certified monday expert | codexsolutionsint.com