You need to befriend the governor of the province you want and they need to have less than 40 loyalty. Being friends with a foreign ruler gives -5 loyalty and inspiring disloyalty gives another -20, so it's usually not too difficult. You'll get a character interaction called "entice governor" which causes the governor to defect along with any neighbouring provinces they control with less than 50 loyalty. It costs a flat 20AE every time you do this and gives you a big relations hit with the country, and they also get a CB on you, but if you're the ally or tributary of a powerful nation they probably won't ever use it.
The Antigonid capital is in Syria, and it looks like they still control part of Syria so that probably hasn't changed. This means their lands in Palestine will be under a governor, and probably gradually losing loyalty because they don't like being ruled by Greeks. This means it probably won't be too long before you can steal them (although there's a bit of RNG involved).
There will probably be more Daidochi wars over time, and the situation will change. Hopefully what will happen is that the Seleucids take the rest of Syria, because again Syria is outside their capital region and will probably end up being disloyal (allowing more land stealing).
If Egypt doesn't take Palestine, they could be a good overlord for you later as you won't be able to take much useful land from them anyway (just part of Palestine and Nabatea once they conquer it).
It's a very RNG dependent strategy. I played in a very similar way while doing Tyrian Purple, and it took a bunch of restarts to get the right conditions, but if you're not invested in meeting particular expansion goals it can be a very chill and relaxing way to play, and you just have to exploit the situation and take opportunities as they come.