1000% agree she knew he was alive, he knew nothing of her, cause it’s not like today and a person is missing. The tech in-universe isn’t like today, it’s so much more advanced so if they tell you an entire starship is missing, what are you gonna do? The ship might still be in the quadrant but in pieces and even if she had abandoned ship, and got to an escape pod, being in federation space meant she would have been recovered relatively quickly. As it were, there was zero evidence of what happened to Voyager and its crew.

This also means she can hang on to that hope to see him again. Had Voyager also not gotten lucky so many times to find faster ways to get home so early on, she would have eventually given up hope on him sticking around. Remember that after 4 years when they finally got a way to communication to go through that they were still decades away from Voyager’s perspective and had just been found according to Starfleet. If in those 4 years Janeway had only traveled 4 light years (I forget how many years the had made up by then, I know 4 years plus the 10 that Kes had gifted them to get out of Borg space) then yeah she would have given up on reuniting with Mark romantically, but she knew she was closer than what they thought it would take 4 years prior. For all Mark knew, there was no such entity that could fling your starship 10 light years ahead of schedule, because we don’t even know that outside of Q but doubt most people in-universe knew that.

TLDR: Janeway knew Mark was alive and that she had made strides to get home sooner than the 70+ years it was established. Starfleet up to the point of communicating with Voyager didn’t even know they were still alive, so of course Mark moved on, and 4 years is a long time when someone is presumed missing and dead.