The Public Record Office of Northern Ireland has upgraded its subscription to FindMyPast so that the 1921 Census for England & Wales is now available to researchers using computer terminals in PRONI's Search Room.
Other databases available on-site for free viewing to the public are the BritishNewspaperArchive.co.uk, Ancestry's Library edition, and the Irish State Papers (from Cengage).
These are, of course, in addition to PRONI's own digitised material from collections held in its archive (see the list of collections here); these can be accessed online via the Internet, no matter where you are.
Unfortunately, there is still no access from PRONI's Search Room to the full database of the General Register Office of Northern Ireland. The dedicated 'GRONI terminals' (ie computers supplied and managed by GRONI to provide access only to the GRONI database), were put out to pasture last year and replacement equipment was expected to be installed and operational by the end of 2022. This hasn't happened and I can't seem to pin down anyone willing to provide an explanation!