You can easily install the new SSD in your Asus B550 mainboard, as it supports at least one M.2 slot with PCIe 4.0 x4.
Whether you need a heat sink depends on whether your motherboard already has one or whether you want to retrofit one.
The heat sink that came with your 1TB SSD is usually designed for this particular SSD and cannot be easily transferred to another SSD, as the dimensions and fastenings do not always fit.
The WD Black SN850X (2000 GB, M.2 2280) is compatible with your mainboard and can be operated with or without a heat sink.
If you value low temperatures, a suitable heat sink is recommended, but it is not a must.
Whether the existing heat sink fits depends on the design - heat sinks for M.2 2280 SSDs are usually universal, but the mounting can vary.
You can therefore order the new SSD without a heat sink and decide later whether you want to retrofit one.
The WD Black SN850X is a very fast and reliable choice for your system.
If you are unsure whether the existing heat sink will fit, check the dimensions and mounting options.
The SSD is compatible with your mainboard and also works without a heat sink.
If you want to use a heat sink, make sure that it is suitable for M.2 2280.
The WD Black SN850X is a very good choice for your project.

Thank you for the quick and competent answers!
What would you install?
I have a Kingston 1TB in there now, but I hear very good things about the WD, is there anything better apart from Samsung.
I read that the 4TB is actually better than the 2TB. I will buy the WD with heatsink, unless someone has a better tip.
Thanks for your time and effort