That is a supposition, right there. How do you know that Trump Force 1 does not have a "SCIF"?

Because as President Trump would always fly via Air Force One. Even when he did campaign rallies he used Air Force 1. AF1 has a SCIF.

I see no reason a SCIF would ever be installed on a private plane

The general idea is that Obama took classified docs to his library. When he did so, WHILE in office (till jan.20 noon) would that mean these docs he took, where declassified by the sheer act of taking them?

No, these documents were not declassified.

The documents in presidential libraries are maintained by the national archives. The National Archives routinely deals with classified information. There is a classified reading room at the national archive in College Park, Maryland.

The documents for the Obama library and the documents for the Trump library are maintained by the national archives.

There are two parts to presidential libraries. One is the maintenance of the documents and this is done by NARA. The other is the museum piece which is done by a private foundation.

Trump did not set up a museum piece but there is a Trump presidential library. The files are maintained at the national archives in Maryland. For presidents who have set up museums, their documents are maintained at National archive facilities close to the museum.

Info on the Trump presidential library can be found here. https://www.trumplibrary.gov/

Here's info on how researchers with security clearances can go to the national archives and view classified information. https://www.archives.gov/records-mgmt/accessioning/research

That is a supposition, right there. How do you know that Trump Force 1 does not have a "SCIF"?

Because as President Trump would always fly via Air Force One. Even when he did campaign rallies he used Air Force 1. AF1 has a SCIF.

I see no reason a SCIF would ever be installed on a private plane