I had purchased Infuse Pro 5, can I get a free upgrade to Pro 6?
If you purchased infuse 5 pro there should be at least a discounted version of 6 pro in the App Store. Otherwise I might wait for infuse 7 to come out early next year. Also you can always get a subscription or purchase lifetime to get all upgrades for infuse.
There are no “free” routes to V6 but you’re current offers for upgrading are here.