The Old Parish Registers are available through ScotlandsDocuments which can only be referenced at a Scottish archive to my knowledge.
Your understanding is erroneous.
The Old Parish Registers are the Church of Scotland's records of baptisms, banns and burials, and it is the OPRs that form the main database on Scotland's People, and can be viewed from home at a charge of £1.50 per page.
What is only available in certain (not all) Scottish archives is the Kirk Session records, which are the surviving minutes of the proceedings of the kirk sessions of the Church of Scotland.
I think the archives where the Kirk Session records can be viewed include the National Records of Scotland Historic Search Room in General Register House, Edinburgh; the Mitchell Library, Glasgow; the Aberdeen City Archives; the Highland Archives, Inverness; and the Borders Archives, Hawick. There may be others I don't know about.