My understanding was that the funds from Brian Acton were a loan to be repaid, though might be wrong. I was unable to quickly locate any information relate to Pavel Durov having any financial relationship with Signal.

Are you suggesting Signal should not repay their debts or the best time to do that is not as soon as possible? If not, regardless of if there’s no interest, that loan should be repaid as soon as possible in my opinion. In my opinion, 990s are public, that loan was publicly acknowledged, and see no issue with a non-profit raising donations or repaying their debts.

All that said, if it was up to me, Signal would have their 990s on their site, annual publicly shared audits, etc. - which to my knowledge they do not.