So the banks had bonds in their balance sheets that went down in price because of the rising interest rates. If they are in need for money, they sell them quickly but don’t get 100%. So basically not all checking account money can be satisfied. In my understanding, this brought down SVB.

The Fed took over these bonds for 100% as a measure of stabilization. There is no issue here because bonds will be repaid for 100% most probably. Basically the Fed is taking over temporary losses of the banks. When the bonds are repaid the negative equity will vanish.