If my house is worth $1M in 2022, I pay tax on that $1M of value. If it goes down in value to $500K in 2023 (and is reassessed), I'd pay tax on $500K value in 2023.
If I own $1B of AMZN in 2022, I'd pay wealth tax on my $1B holdings in 2022, if the market tanks and AMZN is worth $50M in 2023, then I'd pay the wealth tax on $50M in 2023.
Just as with property taxes, a wealth tax is generally annual based on current assets.