in terms of SSR you actually compile vertex shader to do it. (look up code.)
here’s small example of SSR shader-- https://pastebin.com/EkHhfQA1
There are plenty of hacks you actually use to optimize some reflection shaders, as you want to save on performance. So you implement lightmap with specularity, objects, skybox and further away or more complicated objects; and you pretty much compute only particle effects and changing models while other stay in ‘ready’ state.
lightmap in itself doesn’t need to be static image like in its first implementation in quake (it could be 3d scene or object - and viewpoint is calculated by vertex shader and used for SSR.) – if you wanted to play around with technicalities you could say SSR, ambinet occlusion, global illumnation any many more are just lightmaps or vertex shaders hehe