One of the hallmarks of The Flash has been the multiple iterations of Harrison Wells to have appeared throughout the various seasons, each one brought to life by Tom Cavanagh. The current incarnation, tomb raiding adventurer Nash Wells, has been stated to be the only one left, and Cavanagh himself has weighed in on whether or not that is truly the case.
A number of changes were made to the Arrowverse in the wake of “Crisis On Infinite Earths,” but the primary one was the consolidation of the Earths on which the main shows take place. The multiverse still exists, but when Oliver rebooted the multiverse with the power of the Spectre he cut off interdimensional travel, leading to the residents of what is now Earth Prime believing that no other worlds exist.
When Cavanagh appeared on Fake Doctors, Real Friends, a Scrubs rewatch podcast hosted by Zach Braff and Donald Faison, he was asked whether Nash was truly the final Wells, and had this to say:
“Here’s what’s ridiculous about doing a superhero comic show: I run into people like you and I’m just so inferior with my knowledge. You know more than me. I’m not exaggerating, I’m not trying to play dumb. I understand by listening to you that you have a better grasp of the whole thing than I do. I feel like – as you guys know when you do a long-running television show – if there needs to be another Wells, there can be another Wells.”
So, sorry for the non-answer to the question, but to be honest, it’s not an entirely unreasonable response, even for someone actually appearing on the show in question. Since The Flash in particular has frequently dealt with interdimensional travel, it’s been brought up the most, and its characters’ current understanding is that the multiverse no longer exists. As a result, they believe the only version of Wells still alive is the narcissistic Nash as he was the one on Earth-1 when Crisis hit, and outwith that context it appears to be the case.
However, we as viewers are aware that counterpart Earths were also restored, as the coda of the crossover showed the characters of DC’s various past and present TV shows on their own planets with each one numerically identified, while Stargirl makes it abundantly clear that it has an entirely different history of the rise of the Age of Heroes that ran separate from that which grew from the events of Arrow.
So, to summarize, while Nash is the only Wells currently featured on The Flash (unless you count Reverse-Flash once again escaping being wiped from existence), there’s no reason in the future that travel to parallel worlds won’t be opened up, and all the weird and wonderful versions of the character can once again be seen.