The achievement is NOT unobtainable or discontinued
, it can just become unobtainable if you don't know what you're doing and mess it up.
The achievement requires you to make it to the max 'prestige' (Gen 10) WITHOUT buying a certain item (Forged Certification) from the shop
that allows you to skip one of the in-game regen challenges. You will have to do these challenges to 'Regenerate' (prestige). These challenges are, for example, killing a certain number of enemies with a certain weapon or winning a certain number of rounds. Nothing too bad, just a little time consuming. For a more in-depth look at each of the regen challenges, refer to marksman3698's guide for reaching Gen 10.If you buy that item, you will have to start the game from the beginning!
This game is probably a 200+ hour completion so buying that item will force you to start over. I do not know how you would reset your level so that is probably why it is marked as partially discontinued.
The achievement is a grind, but still very much obtainable. You just have to be careful and know what you are doing.