The only way the Packers save significant cap space by holding on to Lowry is him agreeing to take a substantial pay cut.
I'm not sure he's ready to accept such an offer.
The "good news" for the Packers is that besides the workout bonus ($300K), which I believe has to be paid at the end of June, depending on attendance, they aren't pressed into make an immediate decision on Lowry. So unless they need immediate cap relief, they can see what is out there in Free Agency and the draft and make the decision on Lowry after. They may have already begun negotiations with his agent with a message of "here are the terms we are willing to keep Dean at, otherwise we might have to release him".
This odd Covid reduced Cap year is going to create a lot of situations like this. Players and agents are going to have to decide "with the limited amount of money available to many teams, do we just take the one year offer and try to hit some incentives?"
Looking ahead to 2022, the Free Agent Market is probably going to be huge again, since many players will have signed low end one year deals in 2021.