Some of them we already know little bits about/can piece together
Tommy: got his PhD and did the whole dino cloning thing/served as mentor for Dino thunder rangers
Billy: eventually came back to earth, set up Cranston industries and searched for zordon/served as mentor for Dino Charge rangers
if Once a ranger is considered cannon
Kat: Married tommy?
Rocky: became a firefighter
Adam and Alishia: Founded SPA
Zach: Became a congressman
Trini: Killed by Rita
what about the rest/if OAR i not cannon what's your head cannon for MMPR-Space rangers
My head canon theory is that most of the older Rangers revealed their identities after Countdown to Destruction because the Space Rangers did
Jason and Zack (maybe Billy as well) donated their Morphers to let everyone understand their technology to access the Morphing Grid (This how Captain Mitchell and Lightspeed got the Ranger tech to make the Lightspeed Rescue Rangers)
Because of them doing that created not only other ranger teams but straight up organizations
Jason: Probably married Emily and opened up his own autoshop.
Kim: Teaches ballet.
Andros and Ashley: Likely married and live on KO-35.
TJ: Likely cashed in on the fame of being a public identity Ranger.
Cassie: Tried out a singing career.
Carlos: Became a soccer coach.
Justin: Went to college. Later became a teacher.