Summary
Jeffries is the NBA-equivalent of a "AAAA player", someone that is good enough to be outside of the G-League, but not quite good enough to be an NBA player. At 6'5" but strong and athletic, Jeffries is probably best served to be a small-ball big since he hasn't developed enough of an offensive game to play alongside other offensively-challenged bigs. Jeffries needs to either improve his positional awareness on defense to become a rim protector or otherwise disruptive defender, or develop his offensive game, specifically his outside shot, in order to stick around in the NBA.

Jeffries is still only 23, so it's reasonable to be optimistic about his improvement, but he's old enough that the chances of him developing into a legitimate rotation-level player are unlikely.
 
Cap Considerations
Jeffries's $1.7 million salary for 2021-2022 is non-guaranteed, and if he is waived he will become an unrestricted free agent and the Spurs will have no form of Bird rights on him. If he is waived, any team could claim him off waivers since he is on a minimum contract.

If Jeffries 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. It's likely that Jeffries ends up settling for the minimum.