you are one of the most fortunate people have had 400k uni if that is indeed your assets then you become wealthy suddenly I was not as lucky as you could make a deposit in uniswap but I failed trades due to lack of fee-gas I really do not believe that uniswap provide airdrop tokens for free.
If I am not mistaken there is a requirement to claim UNI tokens, I mean if you are an active user on the Uniswap platform then you can receive 400 UNIs for free but you have to claim before September 1st or before the party ends. I personally also did not get the 400 UNI prize & lucky for those who did.