I believe there's an ex-Buddhist poster here who once pointed out that Neoplatonism and Buddhism aren't likely to "mix well"
@CountPeter maybe?
Might be me you are thinking of. Whilst I am not too sure how strongly I still align with Buddhism, I have indeed made posts before talking about their incompatibility.
Depending on when it arrived, I could see it finding a good partner in Neo-Platonicism, which displayed some characteristics which already somewhat leaned in that direction.
Neo-Platonism and Buddhism are very philosophically opposed. There is a lot to cover, but essentially Buddhism grew in reaction to and in opposition to the Brahmanical religion (itself much closer to Neoplatonism), and particularly in its early form.
Before I get into this, it's worth prefacing that it's hard to get a fully definitive "Buddhism" in the same way that we might characterise western religious traditions. For example, we recognise Islam and Christianity to be distinct religions (if part of the same tradition), and yet the theology and philosophy of sects of Buddhism within the same country are world's more different whilst still acknowledging eachother as Buddhist. Pure Land for example (generally) doesn't recognise the ability for people to be enlightened in the modern world, instead looking for intercession on behalf of otherworldly Buddha's that change depending on tradition.
With that big aside, here are some of the reasons the Buddhism is philosophically incompatible with Neoplatonism.
Materialism: Buddhism wasn't in opposition to materialism, just as it wasn't in opposition to transcendentalism. Rather, Siddhartha taught a middle way both ethically (the world is both Nirvana and Samsara) and epistemologically (fitting somewhere between empiricist and rationalist thought). Siddhartha taught a level of connection with the material world strongly at odds with that of most Neoplatonist sects.
This also extended to the nature of existence, with the fundamentals of sunyata (emptiness) being about reality existing as phenomena, the only constant of which is change as opposed to the eternal emanations of Neoplatonism. This is important because...
Siddhartha did not teach that souls exist, which is a big problem for Neoplatonism. More to the point, nothing could exist like emanating forms or absolutes in platonic philosophy, because to the Buddhist world view we are connections between phenomena rather than static points in and of themselves.
This means that stuff like reincarnation is often misunderstood in early Buddhist literature, where it doesn't actually exist. Rather, a clear distinction is made between the brahminical reincarnation (in which we are all ultimately emanations of the monadesque brahma) and rebirth. This is because of Sunyata, or emptiness.
For context, the term itself is used as part of a metaphor using a jar. A jar is a container for something, with it's nature being changed by constantly changing conditions (time, what fills it, what doesn't fill it etc). A jar of peanut butter is not just a jar of peanut butter because it contains peanut butter, but because of all the things it DOESN'T contain at a given moment (like how a jar of peanut butter and jam is itself a new state of being). In turn, the concept of static identity is criticised in Buddhist literature because what defines us (our physical make up, our relations to others, our temporal and geographical location etc) never stop changing, like everything else. Reincarnation doesn't make sense within such a philosophy because the new "person" wouldn't be "you" even if there was a transmigration of the soul.
Instead, early Buddhist thought made the clear distinction of rebirth versus reincarnation. Rebirth is the way our karma (essentially causality applied to Sunyata) echoes throughout history. The Buddhist philosopher Nagarjuna (who was in many ways the Plato of Buddhism and debatable founder of Mahayana Buddhism) described this with the metaphor of a magician who's tricks inspire others to do the same tricks, perpetuating themselves.
Another point is that Buddhism (and this is pretty much true across most traditions throughout history), doesn't really care about a creator. Whilst Siddhartha expresses an attitude that doesn't care about the matter of god's (essentially a position that they too are trapped in samsara if they exist), the stories surrounding him go a step further. In one, he acknowledges not a demiurge, but the straight up source of the universe and still shows them to be stuck within the cycle of Samsara. Mortals are generally depicted to be in a better position to escape Samsara than even the dreamer from which the universe stems.
There's a lot more to it than that, but I don't want to derail the thread too heavily on this
