Assume we have a Wizard who is at least level 13 and can reliably cast Sequester many times (either through acquired spell scrolls, or has acquired enough material components for it to be a non-issue), has a safe place (through the spell Demiplane) to be under the influence of Sequester for many centuries, and has access to the Manual of Bodily Health, Manual of Gainful Exercise, Manual of Quickness of Action, Tome of Clear Thought, Tome of Leadership and Influence, and Tome of Understanding.
Per the item descriptions in the DMG:
…your [STAT] score increases by 2, as does your maximum for that score. The manual then loses its magic, but regains it in a century.
Now, normally this would be a once-in-a-lifetime use, or maybe twice (due to the lifespan of the races), but if a wizard used Sequester on themself, many years can pass without growing older:
…[willing target creature] falls into a state of suspended animation. Time ceases to flow for it, and it doesn’t grow older. You can set a condition for the spell to end [before the spell is dispelled by the caster].
So, assuming that time continues to flow for the magic items, but not for the sequestered wizard, can they study these books and take the necessary long rests, Sequester for a hundred years, “wake” from the Sequester, and then repeat an arbitrary-but-finite number of times for an arbitrarily high (but finite) improvement to their stats?
To end the cycle and escape the demiplane, the wizard would simply Plane Shift out:
…You can specify a target destination in general terms … and you appear in or near that destination.