What percent of circulating supply needs to be staked for the Beacon Chain to be considered minimally secure?

Right now about 10% of all ETH is locked in staking on the Beacon Chain, yes? What does that percentage need to be in order to meet the minimum security threshold? And how soon after the Merge is it estimated that the Chain will reach that threshold? Surely 10% isn't enough...?

And sorry if the answers are obvious... I searched around, but can't find any discussion related to this... Thanks!

Edit: Ok, I finally found one, fairly recent post with some discussion on this, but it's still entirely speculation/opinions... There must be some official maths/research on this somewhere, can anyone point me to it...? Thanks again!