UAE leaving OPEC is like breaking up a workers union. UAE is no longer required to restrict how much oil it exports, and also doesn't have to set a price floor. They're allowed to sell more oil cheaper, potentially at the expense of neighboring OPEC countries.
Which to me sounds like a good thing for the rest of the world?
If you've been involved in an SDO ("Standards Development Organisation" think ISO or the IETF although the IETF would insist that they are not in fact an "Organisation" they will admit to being in effect an SDO) you've probably at least glanced at documents explaining that you absolutely must not do anything which looks like Cartel activity, you can't use the SDO to agree prices, or to cut up territory or similar things. The SDO's lawyers will have insisted they make sure every participant knows about this because they don't want to end up in prison or worse.
However the trick for OPEC is that it's a cartel of sovereign entities. It can't be against the rules because its members are the ones who decide the rules. So Chevron and Shell and so on cannot be members of OPEC but the UAE and Venezuela can.
It probably isn't a bad thing, but let's not overestimate the beneficial effects. The reason oil prices are high right now isn't because of cartel fuckery, it's because of Trump and his war. And oil supply chains are in such chaos because of Trump's war that even if it ended tomorrow it would take markets multiple years to return to a pre-war state.
The bottom line is that oil prices are going to be elevated for years to come, and when oil prices are high, OPEC has nothing to do other than sit back and collect the profits. And thanks to the ongoing solar revolution, oil's days as the world's predominant geopolitical poker chip are numbered; by mid-century OPEC won't be relevant anyway.
Even if this turns out to be true, it would be irrelevant. The reason that oil occupies the geopolitical role it does today is because of its potential to rapidly bring the entire developed world to a halt. Oil will always be in demand because of its many useful applications (and this demand may even grow in absolute terms despite declining per-capita consumption, because the global human population is projected to continue increasing well into the latter half of the century), but as an energy source, by 2050 it will have so many highly-available complements that an oil cartel will be as relevant as a potato cartel.
https://www.cbc.ca/news/world/potato-cartel-fries-tater-tots...
"In 1949, Venezuela initiated the move towards the establishment of what would become OPEC, by inviting Iran, Iraq, Kuwait and Saudi Arabia" ...
Nigeria joined OPEC in 1971.
UAE leaving means UAE can price below OPEC's target and take more of the market. OPEC will have to react and lower prices or concede some of the market.
Does any of this matter if the major players can't ship oil through Hormuz? Who knows...
And while it's true many member exceed targets, it's like speeding on US highways: everyone does it, but anyone driving 20 mph faster than the pack is nobody's friend. Karma will happen.
Recently the UAE faction in Yemen was forcefully reined in by the house of Saud, and OPEC kind of prioritises different things than the UAE, i.e. not pushing profits hard in the short to medium term instead focusing on stability and predictability.
Currently the saudis are trying to resolve the Hormuz issue and the attack on Iran through diplomacy, which the UAE is not exactly fond of and would rather see a violent solution. In part this is coloured by the close relation between the UAE and Israel, both of which share the view that running militant factions in failed states is preferable to orderly international relations between sovereigns. The saudis aren't as keen on this type of foreign policy and in other aspects also not as friendly with Israel as the UAE.
The UAE has been signaling that they don't really want to be a part of OPEC since at least 2020 or so. Them actually leaving was to be expected, the question should have been 'when' rather than 'if'. Iranian retaliations on the UAE and subsequent damage to the reputation of mainly Dubai and Abu Dhabi as well as capital flight probably strengthened the UAE politicians longing to get out of OPEC and start pumping and selling at full capacity to try and make as much money as possible as fast as possible.
If the UAE does not do this it'll be more exposed to credit and currencies besides the US dollar, which they probably find rather inconvenient.
It all depends on how Saudi wants to be seen in the moment and what Trump thinks makes him look better in the moment.
But like, Saudi gave Americans golden planes and extraordinary amount of bribes, so one would assume they were buying something.
Slowly weakening remaining Arab states and setting them up to fight each other.