What is the Palestinian claim of a right of return and is it a valid claim ?

The main bulk of Palestinian refugees were created through the ethnic cleansing of Palestine at the hand of Zionist militias between 1947-1948 and the subsequent establishment of the state of Israel. This campaign of ethnic cleansing took place before and during the war of 1948, and saw approximately 800,000 Palestinians expelled from their homes, and over 530 villages being demolished. Another large wave of displacement and expulsions followed the war of 1967. Israel depends upon the displacement of these refugees and their descendants to maintain itself as an ethnocracy.
As of 2021, it is estimated that there are over 7 million Palestinian refugees worldwide, most of which are registered through UNRWA.
Israel prevents Palestinian refugees from returning because it claims they are a security threat. However, seeing as Israel is a settler colony built on stolen land, it did not have the population numbers to sustain itself. It could only be established by creating new demographic realities on the ground, these new realities necessitated that approximately 80% of the Palestinians in what is today considered Israel be ethnically cleansed to maintain a demographically stable Zionist ethnocracy. In short, Israel can only exist because millions of Palestinians are scattered refugees all over the world, simply because they are not Jewish.
As with any other refugee population Palestinians are entitled to return to their homes. There are also United Nations resolutions specifically affirming the Palestinian right of return. Israel, however, contends that no such right exists.
Palestinian refugees are special in the sense that they are overseen by the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) rather than the United Nations High Commissioner for Refugees (UNHCR). This is because (UNHCR) did not exist as an organization when the ethnic cleansing of Palestine occurred. This, however, confers no special privileges to Palestinians, and can in fact be detrimental to Palestinian refugees compared to refugees from other contexts.
According to the official United Nations website:

Under international law and the principle of family unity, the children of refugees and their descendants are also considered refugees until a durable solution is found. Both UNRWA and UNHCR recognize descendants as refugees on this basis, a practice that has been widely accepted by the international community, including both donors and refugee hosting countries. Palestine refugees are not distinct from other protracted refugee situations such as those from Afghanistan or Somalia, where there are multiple generations of refugees, considered by UNHCR as refugees and supported as such. Protracted refugee situations are the result of the failure to find political solutions to their underlying political crises.

The expulsion of the Palestinians forms a cornerstone of the question of Palestine and the Palestinian revolution. The refugees expelled by Israel still languish in refugee camps simply for not being Jewish. For any lasting solution to materialize justice must be taken into account. There can be no justice without the right of return.
Further reading:
1) The Right of Return in International Law:* All refugees have a right to return to areas from which they have fled or were forced, to receive compensation for damages, and to either regain their properties or receive compensation and support for voluntary resettlement. This right derives from a number of legal sources, including customary international law, international humanitarian law governing rights of civilians during war, and human rights law. The United Nations’ Universal Declaration of Human Rights states in Article 13(2) that “[e]veryone has the right to leave any country, including his own, and return to his own country.” This is an individual right and cannot be unilaterally abrogated by third parties.* In December 1948, following Israel’s establishment and the attendant displacement of more than 750,000 Palestinians from areas that fell within its control, the UN General Assembly passed Resolution 194, which states:> “refugees wishing to return to their homes and live at peace with their neighbours should be permitted to do so at the earliest practicable date, and that compensation should be paid for the property of those choosing not to return and for loss of or damage to property which, under principles of international law or in equity, should be made good by the Governments or authorities responsible.”* The Palestinian right of return has been confirmed repeatedly by the UN General Assembly, including through Resolution 3236, which> “Reaffirms also the inalienable right of the Palestinians to return to their homes and property from which they have been displaced and uprooted, and calls for their return.”* The Palestinian right of return has also been recognized by major human rights organizations such as Amnesty International, which issued a policy statement on the subject in 2001. It concluded:> Amnesty International calls for Palestinians who fled or were expelled from Israel, the West Bank or Gaza Strip, along with those of their descendants who have maintained genuine links with the area, to be able to exercise their right to return. Palestinians who were expelled from what is now Israel, and then from the West Bank or Gaza Strip, may be able to show that they have genuine links to both places. If so, they should be free to choose between returning to Israel, the West Bank or Gaza Strip. ‘Palestinians who have genuine links to Israel, the West Bank or Gaza Strip, but who are currently living in other host states, may also have genuine links to their host state. This should not diminish or reduce their right to return to Israel, the West Bank or Gaza Strip.https://www.amnesty.org/en/latest/news/2019/05/israels-refusal-to-grant-palestinian-refugees-right-to-return-has-fuelled-seven-decades-of-suffering/* According to a statement issued by Human Rights Watch in 2000:> HRW urges Israel to recognize the right to return for those Palestinians, and their descendants, who fled from territory that is now within t