One of the co-bbeg's in my campaign is an aboleth, the party has reached a point where its reaching out to them individually to try and trick them/win them over ect. The party isn't aware that its an aboleth they're facing yet, and i was wondering about some ideas for creepy aboleth theming i could put into their meetings with it

I'm assuming this is needing help with the visions the group gets from the aboleth. If not, and this is about the actual meeting/fight with the aboleth, skip this long answer and write underneath it, I'll try to think of more combat focused elements.

I would go with the typical deep water eldritch horror, that's what I play them as, it feels like that's the origin.

For the depths of the ocean:
Deep unending darkness, the coldness surrounding you, feeling like you're floating, maybe even the pressure of being so deep underwater.
Tentacles, rows of teeth, red, almost glowing, eyes staring into you, showing knowledge far beyond your lifetime and cruelty, that's the aboleth for me.

You can recommend they search a library to find a monster that fits that descritpion, if you want them to find out.

If you want to give them more information on the aboleths abilities, you can give them a dream where they are underwater, see up and see the light coming from the surface, and they swim up, only realizing in the last moment that they have no problems breathing underwater and for them to choke on the air, and having to swim down where they see monsters move around, and hands of people who suffered the same fate reachign for them (yeah, horror). It shows that Mucous Cloud poison from the aboleth, and the Enslave Action.

The lore on Aboleths can offer some insight. They are smart (int 18) and have perfect memories that stretch back eons. They plan intricately with lots of deception and misleading to reach their ultimate goals.

"Aboleths’ minds are treasure troves of ancient lore, recalling moments from prehistory with perfect clarity. They plot patiently and intricately across eons. Few creatures can conceive of the extent of an aboleth’s plan.

Gods in the Lake. Aboleths dwell in watery environments, including ocean abysses, deep lakes, and the Elemental Plane of Water. In these domains and the lands that adjoin them, aboleths are like gods, demanding worship and obedience from their subjects. When they consume other creatures, aboleths add the knowledge and experiences of their prey to their eternal memories.

Aboleths use their telepathic powers to read the minds of creatures and know their desires. An aboleth uses this knowledge to gain a creature’s loyalty, promising to fulfill such wants in exchange for obedience. Within its lair, the aboleth can further use its powers to override senses, granting creatures, such as its followers, the illusion of promised rewards.

Enemies of the Gods. The aboleths’ fall from power is written in stark clarity on their flawless memories, for aboleths never truly die. If an aboleth’s body is destroyed, its spirit returns to the Elemental Plane of Water, where a new body coalesces for it over days or months.

Ultimately, aboleths dream of overthrowing the gods and regaining control of the world. Aboleths have had untold eons to plot and to prepare their plans for perfect execution."

So, in your world, what is the goal of this Aboleth? Long term, it may be related to weakening the powers of the gods. One way it could do this is to encourage factional fighting between as many different god factions at the same time as possible while simultaneously causing or encouraging disasters - earthquakes, floods, sink holes - for the civilian population so that they begin to lose faith in the gods ability to help and protect them. Over time, these disenchanted commoners might be encouraged to turn to the Aboleth who could choose to "prevent" these disasters. (SInk holes are caused by using water to weaken surface soil ... similarly, an earthquake or landslide could be caused by manipulating sub surface water to destabilize the surface, floods would be easy for an Aboleth ... their goal would be to turn the population away from the gods).

If the Aboleth wanted to gaslight a group of adventurers (or more than one), they could pretend to be a secret spy who finds evil doers and relays that information to members of the party. Destroying the followers of any god is a win for the Aboleth. Similarly, the Aboleth might choose to spread misinformation about the party to other religious groups that might then oppose the party and get killed in the process. Perhaps posing as a low level wizard with access to some sort of telepathic device would work for the Aboleth in this case. They would need to be careful to not reveal their nature as the party takes actions the Aboleth wants based on their communications.

In addition, the Aboleth could pretend to accidentally reveal that the followers of a good god have been infiltrated by an opposing cult. Encourage the party to leave them alone in the hopes that the party doesn't listen then act disappointed when the party wipes out the "evil" followers while secretly rejoicing.

Aboleths also can't die so personal risk only represents a delay in their plans, not the end of them. In addition, as Lawful Evil,  they will likely work with other Aboleths so if one's scheme is discovered there might well be another Aboleth to take over.

There's an episode of the Netflix show Love Death and Robots called "Beyond the Aquila Rift" in which a guy slowly realizes he's living in some kind of simulation and his girlfriend is part of it, leading to one of the most horrifying eldritch horror reveals ever at the end. 

Now, that episode is HELLA explicit and I don't recommend fully copying it in your game, but you can use the spirit of it. Maybe have one of your players start hearing voices from either a long list love, damsel in distress, or small child (creepy children are always worth some scare points) that are somehow trapped in the dungeon. Have the voice speak to them in their dreams, drawing them in slowly, and when they finally reach it, have the aboleth waiting instead in all it's weird gross glory. 

again with the deep water horror theaming, you could have the aboleth send them dreams of drowning, with it ending with the aboleth almost saving them, getting closer and closer each time, so that when they meet the abooleth, they think its freindly. MUAHAHAHAHAHAHAHAHAHA!