How do LineageOS security updates work when the official updates from Google cease?

I recently bought a Google Pixel 4a. The link from the title outlines that security updates from Google will soon be ending for the Pixel 4a (though there was a surprise update in November, but no further updates are expected).

Yet, in spite of that, I assume that LineageOS security updates will continue for this phone, since for a variety of other older phones they have continued. But, I wonder, how will this be achieved? Is there information on how LineageOS creates and releases security updates for the devices that it supports?