The total BTC balance on exchanges continuously decreasing since 2020. This shows that investors are withdrawing and storing their BTC in hardware and cold wallets. They are accumulating BTC for long term. Less BTC on exchanges means less selling pressure.
That must be a right interpretation of level of bitcoins are being left with exchanges. Moreover, there are lots of initiative on not using exchanges and web wallets for security reasons which might be having some impact in long run why we are not seeing exchange BTC balances are diminishing still anyway people prefer to hold on their mobile/computer/paper/hardware wallets which must be a good thing in all sense.
I think Facebook is not the only company that is suspected to have already accumulated Bitcoin. There are probably more of them that are also hoarding in silence.
There are less possibilities as awareness on bitcoin's future must be very low in last 3 to 5 years but if they have planned after bitcoin setting ATH around $20K then they might be holding very low mount given that BTC prices and their level of risk taking money for a secret investments.