Under GDPR it is illegal.

> Data subjects must be allowed to withdraw this consent at any time, and the process of doing so must not be harder than it was to opt in.

Source: https://en.wikipedia.org/wiki/General_Data_Protection_Regula...

There is also FB specific:

> In November 2023, Meta introduced a binary ‘Consent or Pay' advertising model. (…)

> The Commission found that this model is not compliant with the DMA, as it did not give users the required specific choice to opt for a service that uses less of their personal data but is otherwise equivalent to the ‘personalised ads' service.

Source: https://ec.europa.eu/commission/presscorner/detail/en/ip_25_...