What happened to QGIS 2.x LTR?

It's not temporary. I know that people hate change, but that's the way it is. QGIS 3.4.5 replaced 2.18 as a LTR. You can find older versions here: http://download.osgeo.org/qgis/

For Lizmap, they plan to release a version 3.3 soon to be compatible with QGIS Server 3. It seems they need to wait for the QGIS 3.4.6 bugfix release (March 22th according to the roadmap link above). It's true that Lizmap 3.2 is not fully compatible with QGIS 3.

You are welcome to give your feedback on the link below about Lizmap 3.3: https://github.com/3liz/lizmap-web-client/issues/1075

QGIS 2.18 was replaced by the first 3.x LTR-version but you can still download and install 2.18 with the OSGeo4W-installer. Just search for the term qgis218 in the installer.