According to the
DHS REAL ID Frequently Asked Questions for the Public:
Starting October 1, 2020, every state and territory resident will need to present a REAL ID compliant license/ID, or another acceptable form of identification, for accessing Federal facilities, entering nuclear power plants, and boarding commercial aircraft. This is what we call “card-based” enforcement. The card, itself, must be REAL ID compliant unless the resident is using an alternative acceptable document such as a passport. The Act does not require individuals to present identification where it is not currently required to access a Federal facility (such as to enter the public areas of the Smithsonian) nor does it prohibit an agency from accepting other forms of identity documents other than documents from non-compliant states (such as a U.S. passport or passport card).
The USPS will continue to accept non REAL ID compliant identification documents.
I highly doubt that individuals summoned for jury duty at federal courthouses will be required to present REAL ID compliant documents; that will make it too easy to evade subpoenas or jury service. For what it is worth, I don't recall having to present any form of ID when I reported to jury duty at the United States District Court for the Central District of California.