Since Jack was on the initial 53 man roster his entire salary for 2021 is guaranteed (not just the $7M shown on overthecap). But that is the only guaranteed money on his contract.
If the Rams traded for Jack and found a way to create enough cap room to fit his remaining salary ($5.28M) they could cut him after this season with no dead money to deal with.
However, if they converted that $5.28M to a signing bonus and spread the hit over 5 years then he would have a $1.056M cap hit this year, and if the Rams cut him they'd have to absorb the rest of that bonus ($4.224M) as dead money down the road.
If the cut came before June 1, 2022 then all of it would go against the 2022 cap. If they designated him as a post-June 1 cut then $1.056M would go against the 2022 cap and the remaining $3.168M would go against the 2023 cap.
AlbaNY_Ram