I read some old threads about lost Bitcoins ND this question has been on my mind ever since
If the lost Bitcoins were for instance recovered will the price of Bitcoin drop because in theory it would affect the amount of Bitcoin in circulation which will lower it's price . I saw in those threads that lost Bitcoins are considered a donation to the Bitcoin network. so if my theory is correct then we should be happy those Bitcoins were lost.
Lost bitcoins are not a voluntary donations to the network. They are involuntary. Irresponsible storage or the neglected necessity to take care of how you store your Bitcoins is one of the reasons that they will never be able to be recovered. I doubt many of those who lost their coins voluntarily destroyed their access to them.
There will never be a case where all lost Bitcoins suddenly become available to their owners, so there is no need to theorize how much the price would drop if that were to happen. Though yes, the price would drop as instantly a lot of Bitcoin would enter supply rapidly.
Should we be happy? Not really. It's better that Bitcoins are circulating and continued to circulate since that period of time. It creates more ecosystem activity, it creates more use-case and it makes the network more active. Is it economically beneficial right now that these coins are unlikely to ever be circulated again? Sure.
There's no such thing about donation because those coins are totally lost in void and there's no way on getting those coins back unless if those privatekeys would be able to retreive or would be seen again then for sure
those coins would really be get on, considering on how long it had been idle then its impossible for its owners not to sell out on the time that they would really be getting a hold of it.

Lots had been even trying to bruteforce a particular wallet but still failed up and this do proves out on how secure Bitcoin is. This is why if you do own Bitcoin then it would really be just that a common sense
on storing up those keys on a secure place but never ever tend to forget those keys because once those things are lost then say goodbye into your wallet and coins inside it.