All perfect praise be to Allah The Lord of The Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
It is forbidden for a Muslim to promote or advertise usurious banks and financial institutions that deal in Riba (The excess or increase on a loan or in any exchange, specifically when it is considered an unjust or exploitative gain), as this constitutes assisting in sin and facilitating its means. Allah The Almighty Has Prohibited this, Saying (What means): "And cooperate in righteousness and piety, but do not cooperate in sin and transgression. And fear Allah; indeed, Allah is severe in penalty." [Al-Ma`idah/2]. The prohibition of Riba is well established in Islam. As Allah Says (What means): "Those who consume interest cannot stand [on the Day of Resurrection] except as one stands who is being beaten by Satan into insanity. That is because they say, 'Trade is [just] like interest.' But Allah has permitted trade and has forbidden interest. So whoever has received an admonition from his Lord and desists may have what is past, and his affair rests with Allah. But whoever returns to [dealing in interest]—those are the companions of the Fire; they will abide eternally therein." [Al-Baqarah/275].
There is no sin in dealing with those whose wealth is mixed between lawful and unlawful sources, or whose wealth is mostly haram (unlawful), as long as the haram portion is not specifically identified. It is permissible to accept their donations and gifts, provided that this is not tied to promoting or advertising the donor.
Moreover, Sheikh Al-Islam/Ibn Hajar Al-Haytami was asked: "It is well-known that Jews and Christians deal in the sale of alcohol and engage in Riba, among other things. Is it permissible to interact with them and accept their gifts? And what about dealing with someone whose wealth is mostly haram?" He replied: "As long as the haram (unlawful) portion is not specifically identified, it is permissible to interact with them and accept their gifts, for the Prophet (peace be upon him) accepted their gifts. However, if it is confirmed—such as seeing a non-Muslim selling alcohol, taking its price, and then giving it to a Muslim to settle a debt or otherwise—then it is not permissible for the Muslim to accept it, as stated by the two Sheikhs (scholars). The same applies to consuming the wealth of oppressors and those whose wealth is mostly haram—it is disliked unless the haram portion is known." [Al-Fatawa Al-Fiqhiyyah Al-Kubra/vol.2/pp.233].
As for thanking usurious banks or financial institutions in return for their support, the ruling varies depending on its nature: If the thanks is verbal (to the management) or written (such as a thank-you letter), there is no sin in it. However, if the thanks involves publishing advertisements, videos, or promotional posts, it is not permissible, as this constitutes advertising and promotion.
In conclusion, there is no sin in accepting donations from usurious banks and financial institutions if they do not require promotion or advertising in return. If the donation is conditional upon any form of promotion or advertising—including thanking them through posts, ads, etc.—then it is haram, as this constitutes unlawful assistance in sin. And Allah The Almighty Knows Best.