I’m 65 years old with 4 retirement accts. 2 Roth IRAs, Roth 401K & 1 traditional 403b. 1 mill in every acct and cash out. Are you taxed on 4 mill tax bracket or 1 mill?

Roth's are after-tax money and so there will be no tax consequences for Roth distributions.   Only the Traditional account will be taxed.   I would suggest  spreading the distribution over several years to lower the tax on that.   Withdrawing the entire amount in 2020 would put you in the 24% tax bracket plus any state tax.

If you have two Roths at 1M each, unless you are some serious distress situation,  like your grandchild's been kidnapped, it's crazy to cash them out.

One million distribution from a traditional IRA  puts you in the highest bracket. plus an extra 3.8% Net Investment Tax on any capital gains.

Q. Do withdraws from Roth Accts count on determining your tax bracket in a traditional account?

A.  No Roth distributions are not taxable.

Q. Are you taxed on 4 mill tax bracket or 1 mill?

A.  4 mill. Or more accurately, you total distributions for the year, not counting tax free distributions from Roth.

As others have suggested, the standard advice is to leave money in the Roth accounts to continue growing tax free.

Another strategy, if you don't need the money, is to convert traditional IRAs to Roth; converting only enough to be taxed at the lower tax rates.  The converted money, now in a Roth IRA, also grows tax free.