The TVA is a mysterious organization that made its Marvel Comics debut in 1986. The bureaucratic group monitors the Multiverse to ensure timelines aren’t being altered in any way. If the past or present is being changed, the TVA takes action, which is why they set their sights on Loki after he acquires the Tesseract. Historically, the TVA has had many run-ins with Nexus Beings, as has another group referred to as the Time-Keepers. The rare group of Nexus Beings, including Scarlet Witch, has been known to be monitored by the TVA due to their capabilities.
There’s always a chance the TVA will show up in WandaVision as a way to set up their presence in Loki. With Wanda and Agatha’s potential of affecting the past or present by altering reality as Nexus Beings, the TVA could show up to shut them down if S.W.O.R.D. fails to do so. On the other hand, the Nexus antidepressant commercial could be a nod to the Nexus of All Realities, a cross-dimensional gateway that allows a traveler to reach any and all realities. Loki has been known to use similar kinds of portals in the MCU, and a similar gateway may be integral to his time-traveling in the forthcoming series. Either way, the mention of Nexus seems like more than a coincidence.
Originally from https://screenrant.com/wandavision-nexus-brings-commercial-loki-time-variance/