I'd like to see a list of warning severity codes produced when importing an ArcMap document into ArcGIS Pro and their solutions but haven't found such a list. I've done a search on severity code 20007 and it pulled up this site 20007: Layer contains a multilayer line symbol whose symbol widths may result in aliasing—Publish se...
but this site isn't for "importing warning messages" it just happens to be the same warning code.