See this guy?

Say hello to Superman of Earth-22.
This is a version of the Man of Steel who decides to come out of retirement due to the world’s metahuman population growing more reckless with every passing generation. While this Superman might show a little more grey with his spit curl, his many decades of superheroics have provided him with more time under Earth’s yellow sun than any of his younger counterparts.
Having the better part of a century’s worth of yellow solar energy stored in his Krypronian cells has increased his invulnerability to the point where even Kryptonite, the one physical substance that could kill him, has lost nearly all of its effectiveness against him. Even the Lex Luther from Mark Waid’s famous graphic novel “Kingdom Come” has lamented this fact.
A perfect example of Earth-22 Superman’s interactions with Kryptonite was shown when he was accidentally sent to a parallel universe city of Metropolis and found himself in the middle of a terrorist attack that had befallen that worlds Daily Planet. Even though it wasn’t HIS Daily Planet, Earth 22 Superman decided he couldn’t stand by and let innocent people get hurt.
Once at the scene, the Man of Steel showed little trouble diffusing the situation even as the terrorists detonated a Kryptonite tear gas bomb. This older and more experienced Superman simply shrugged off the Kryptonite tear gas with one or two light coughs, musing to himself how it still makes his eyes sting. Undeterred by the Kryptonite, Earth-22 Superman apprehends the villains responsible for the attack on the Daily Planet with as much effort as it would take an adult to subdue a group of temperamental toddlers.
While not resistant through repeated exposure, it is possible for some Supermen to grow even stronger from years spent under the light of a yellow sun and, as a result, less debilitated by the glowing green remnants of his homeworld.
No. He shouldn’t.
Why… Because his body actively draws in radiation from Kryptonite.
For Superman to become immune then he would need to improve his mental control over his powers, to the point that when he began to feel he was drawing in Kryptonite radiation he would simply block it off.
That would make Superman completely immune to at least Green K. Even if not other types like Red, Blue, Black, Indigo, and Golden K.
Red K and Black K if Superman could control the Kryptonite energy that enter his body, they could be used by Supes to actually improve his control over his powers, increase his power level, and even gain access to those powers he has but he still can’t access them.
Superman can resist the effects of Kryptonite radiation better than most kryptonians, really because he has been exposed to Kryptonite more times.
Which is why when a much less experienced Supergirl gets mind controlled by Darkseid and Superman needs to take her out without hurting her too much, he actually puts a Kryptonite ring and then one punch knocks out Supergirl.

For example. When Superman for an entire year he was mentally suppressing his powers in their entirety, Kryptonite Man comes along and Clark Kent feels no effects whatsoever from the Kryptonite radiation being emitted.
That was because he was blocking off his powers completely. Meaning even Kryptonite radiation wasn’t being absorbed.



But when Supergirl enters the scene the Kryptonite radiation being emitted by K-Man was gradually weakening her.


So it has been shown that Superman can block off absorbing energy and thus getting his kryptonian DNA empowered enough for his powers to work at all.
But what he hasn’t shown is the ability to be empowered and select the types of energy he wants to absorb and those he doesn’t want to absorb.
And while that is so then Superman only other option to become immune to Kryptonite, is to dive into the sun, and focus on improving his powers to the point he’s completely immune to it for good.
Which will obviously never happen, because if writers gave that level of control over his powers, to Superman or any other kryptonian then writers would no longer have any easy exploits to use against kryptonians.
Even Red Sunlight would no longer depower them.
Meaning all of Superman opponents would need to either be powerful enough to actually beat him, or possess technology advanced enough to actually beat him.
Which would require something Superman writers aren’t known for having… Creativity!