You are probably looking for Lightroom Classic. There is a naming confusion with the Lightroom products. Lightroom (the cloud version) doesn't have all the features that Lightroom Classic has. Probably the reason there is no web gallery function in Lightroom 5.5 is that your images are already in the cloud. But then, I'm primarily a user of Lightroom Classic so don't quote me.
Please post your System Information as Lightroom Classic (LrC) reports it. In LrC click on Help, then System Info, then Copy. Paste that information into a reply. Please present all information from first line down to and including Plug-in Info. Info after Plug-in info can be cut as that is just so much dead space to us non-Techs.