How should I remove a tyre that's stuck to the rim with old sealant?
Before looking for a product to solve the problem, try this. Many tubeless rims grip the tire very tightly when one is just trying to push the tire very inwards to unseat it. The trick is often to push the bead section more straight down in the direction of the rim well, with a slight scooping motion inward.

Sealant isn't glue and doesn't have all that much tensile strength. It's usually the case that you're more up against the mechanics of how the bead locks in place.