To my knowledge, correct me if I’m wrong but this is also what I know as it does not make sense when interest is knowingly haram to be given towards a mosque
When interest has no barakah in it, how can this be donated towards a mosque? For example, how can the earnings from selling alcohol be given towards a mosque. It defeats the purpose of gaining rewards from donating considering zakat is one of the pillars and Islam emphasise the importance of giving charity.
With the knowledge of interest being haram, using this towards a mosque makes the person sinful and accountable for this action. This adds on to why it would be pointless to give interest money towards a mosque as rather than being rewarded, they would be held accountable.
It was on his instagram on his Q&A, nothing official so don’t take my word for it until something concrete is given. but I have a good memory and was hoping someone may know something about it 
yh I agree, I guess, we could look at a lens of… there will be no barakah for HIM in terms of money wise when you donate and you are not really rewarded for it. And we know of the statement of the prophet PBUH that charity does not decrease your wealth. so… you know, maybe no barakah to him, but what issue is there for the masjid himself. They don’t know, rizq is being provided for them. Who knowwssss!
Highlighting the story of the Quraysh - even the quraysh had ensured to only use pure money to build the Kabah, even if it may be permissible to use interest money, it is something to avoid entirely in honour of respect of the houses of God as the mosques should be built with halal money only.
Ohhh his fatwagram. Thanks anyway
Before giving you’d have to take, meaning the interest you gain and now using to build a mosque is still classed as haram. It’s one thing if you was not aware of this, however if you are then you would know that it is one of the major sins. Dealing with riba is as if you are declaring a war with Allah (swt).