Both get half of each of the disputed areas lengthwise?
This wouldn't work because along Aksai Chin, it wouldn't be acceptable to China and along Arunachal Pradesh, it wouldn't be acceptable to India.
The main solution is the one China has been offering since the 1950s - Aksai Chin is Chinese and both sides formally demarcate the Ladakh side dispute with China's offers since that era or whatever version of it, arguing over 1% or 2% of entire disputed area so it's not as important as demarcating and settling. India refused in the 1950s and still refuses to demarcate. China formally stops claiming Arunachal Pradesh as the Ladakh side dispute is settled. I think China is more than happy to do this because, well it's been suggesting this since before China made a claim on Arunachal Pradesh. The main reason that I suspect for China to make a claim on Arunachal Pradesh is to pressure India to stop claiming Aksai Chin.
The history of this basically goes:
1. China under the Yuan dynasty invaded and annexed Tibet (this was well before European colonialism btw for those who aren't aware of history).
2. The land that is
today's Aksai Chin was administered under the Kingdom of Tibet. As China incorporated Tibet (however one wishes to call it let's call it annex here), China administered Aksai Chin since the Yuan dynasty.
3. China went through many periods of internal warring and dynasties and every time there is weakness in the center of power in China, Tibet attempted to break away.
4. During China's revolution period and civil war period of the 20th century, Tibet wanted to break away and the idea was sort of supported by China's adversaries. Tibet did not manage to break away and as the civil war resolved with KMT escaping to Taiwan and calling themselves the Republic of China, PRC maintained rule over Tibet. It's important to note for context that India during the 20th century has already at the conclusion of the century, annexed multiple kingdoms that were independent of the new India. At this point in history, the USA has annexed many parts of Mexico to incorporate into California and Texas. What I'm trying to say is that if China is a "bad guy" for annexing, keep in mind that this was done during the Yuan dynasty under Mongol rulers. Throughout this time, Western powers have done much more "annexing". Tibet can be "freed" rightfully
less so than Australia should be "freed" of Anglo rule, Canada should be returned to natives and the USA... well go figure.
5. India is a new country in 1950s during the initial confrontation and disputes on the only source of dispute (Aksai Chin area), China is a country going through revolution and just finished civil war and WW2. The British invited both sides to demarcate this stretch of land that no one previously settled in or used properly. China did not recognise the legitimacy of the British being involved due to viewing it as an imperialist power and having no genuine intentions so did not attend the meeting. The British and Indians simply then drew their own lines as they considered "fair" and "fit" and those included Aksai Chin as part of India. China disagrees and there is the beginning of the Ladakh side dispute. Made more complicated after Pakistan and the history following British India -> India transition.
6. India refused to stop claiming Aksai Chin because there is a false legitimacy from the British India unilateral demarcation during the transition to independent India. In an effort to mirror what China considers India's unilateral claim making, China also made a claim on a piece of land that was administered by India since day 1 (to use a figure of speech) and that piece of land is a stretch along Arunachal Pradesh which China knows is strategically worrying for India due to what's commonly referred to as the "chicken's neck" since Bangladesh became independent of India.
So if India stops claiming Aksai Chin, I personally think China would stop claiming Arunachal Pradesh since that claim was made to mirror India's claim of Aksai Chin. This of course isn't a known certainty but it's pretty obvious. Furthermore, I think that China has no desire to keep these dramas going and potentially flaring up every once in a while. China dislikes it. India cannot possibly prefer having it either BUT India has in more recent years, politicised these aspects of tensions and confrontations with China with the backdrop of ... well let's just say the obvious geopolitical shifts and grand power struggles happening. It has been militarising Hindu extremism and letting go of a claim that Hindu extremists and various bhakt varieties alike have been taught to hold close to their hearts in the context of India's "competition" with China, well that wouldn't work out for any Indian leader. Hence they are damned in they do, damned in they don't and right as things are is a comfortable place ... considering the alternatives that they have tried, Amit Shah declaring to Indians that India will "pay with blood" to get Aksai Chin during a speech back in 2019 (which btw Indian media has now scrubbed this of because it's a piece of evidence they had the desire to capture it in 2020).
Not going back to the Ladakh crisis discussions which have been covered n^n times in the Ladakh crisis thread, to answer the question is there a solution? Yes but is there a realistic one where Indian PM can actually perform as China has been waiting for them to do? Not really. China could cede Aksai Chin to India like China has done with some of the Stans and Russia wrt initial border disputes during the 20th century.
The tricky thing with borders is that as a country changes like these two have during their history with colonialism and civil war invasions etc, different ruling parties, different systems, different generations of leaders, will have their own designs on it. ROC's borders for China are much greater than PRC's. If the KMT won the civil war, China would have a lot more land in the Stans, in Russia, huge swathes of Mongolia, and demanded more from India in southern Tibet, not just Aksai Chin's borders but much further beyond, at least to PRC's "ideal" borderlines on the Ladakh side (many kilometers further than PRC's demarcation border offers since 1950s).
In time, these sorts of land disputes become increasingly pointless, non strategic, counterproductive. Resolution depends on how well these two countries develop. This Ladakh dispute is relatively worthless land in terms of natural resources and to China is also relatively non strategic. It is more strategically important for India due to proximity to Kashmir and Pakistan and of course its proximity to New Delhi.