First, note that Estate Planning and the Fool is an excellent resource with many experienced posters. A great place to go for specific answers.
https://discussion.fool.com/contacting-others-post-death-3504908…
First question is where are you on the estate tax issue. The current exemption is $11.8+MM. That’s large enough that most of us don’t have to worry about it. That law does expire in 2025. There has been discussion of reducing the exemption to lower numbers. If your assets exceed the exemption, by all means go see a professional to work out the best plan for you.
Most assets are inherited on stepped up basis by your heirs. That means they receive all of your paper profits tax free up to that $11.8MM limit. Their cost basis becomes the market value of the assets on your date of death. (Congress has discussed collecting capital gains on the gain over $1MM but so far has not come up with the votes needed to pass it.)
This does mean its to your advantage to accumulate investments with paper profits in taxable accounts as they will be inherited tax free. (But of course keep an eye on pending changes in the law.)
Gains in your IRA, 401k, etc are taxed at ordinary income tax rates. And your heirs must pay the taxes when they inherit. So of course work down those values as best you can. Roth conversions is a good strategy. Funding 529 plans for family members can also work. The limits are huge these days. The heirs pay taxes on the gains at their rates. The funds are not part of your estate. Start early to allow funds to grow.