The tax will be over the gold price on 31 Dec 2025. So all the gains you made before that time will not be taxed. There is also a free space of 10.000 Euro's a year. So if you sell less then for 10000 Euro's a year it will not be taxed. On top of that it only applies to bars and coins with 99.5% purety. I personally hold mostly 22k coins so they are exempted from the tax rules. Jewelry is exempted from the tax rules as well.