OK, so I am following upgrade instructions, so far so good. Currently updating system.
A couple of points:
I wanted to stay on perl 5.28 which was available some time ago from a kit, so had to unmask perl and ~20 perl virtuals, don't know if there is a file somewhere with such a list already
Had to unmerge a number of xorg proto packages which had file collisions with one updated xorg proto package.