Summary
Porter was once a first round (even late lottery, to some) prospect, but has dealt with injuries throughout his young career and has yet to make an impact. He has barely played in the NBA, and even only has nine G-League games under his belt. In those games, he hasn't produced much.
Porter still has a chance to turn things around as he's still only 21 and has some skills for a big.

Due to the Grizzlies already not having many open roster spots, I expect them to move on from Porter. He may still get some flyers from other teams as a free agent, but it will likely be only non-guaranteed offers until Porter can prove he can stay on the court.
 
Cap Considerations
Porter's $2 million salary for 2021-2022 is non-guaranteed, and if he is waived he will become an unrestricted free agent and the Grizzlies will have no form of Bird rights on him. If he is waived, teams could claim him off waivers, but would need to fit his salary within cap space or an exception to do so, as his contract doesn't fit within the minimum salary exception as it was a three-year contract.

If Porter becomes a free agent, other teams will have multiple ways to sign him as even teams without cap space could possibly use either of the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE to sign him. However, I don't expect any offers for Porter to be above the minimum.