The Federal government is not allowed to hold, or control ANY land other than what is listed under article 1 Section 8 of the UNITED STATES constitution.
If you repeat something often enough and use enough CAPITALS, it will eventually become true.
The section in question addresses the power of Congress to exercise exclusive jurisdiction over territory within a state purchased with the agreement of the state legislature.
Public, federally owned lands within a state are not under the exclusive jurisdiction of Congress. If I kill somebody on BLM or National Forest land, it’s a state crime, not a federal crime. AFAIK, anyway.
Then why the need for Article IV, Section 3, Clause 2?