Cut the affected boards out and replace them. After that long, the
finish will have been eaten away by the urine and it has soaked
through the flooring (and probably the sub-floor as well), and nothing
you can do will get it all out.

When remodeling, that has certainly been my experience. The only other
thing I have done is strip the floors in the room, then stain them a
different (much darker) color to mask the stain. But on careful
inspection, the offending stain was still seen. No amount of
neutralizer, stain remover, etc., made for urine treatment worked 100%.

In retrospect, I think now it would be easier to go buy some new
laminate floor or the new hardwood floors and just floor over the whole
thing and make a stepped threshold into the room.

Of course, if the flooring is totally trashed, you could carpet.

Robert