The OP didn't say what the rest of his investment portfolio looks like. Most people employ an asset allocation strategy. To decide how best to deploy $200K sitting in a MM account, it is helpful to know how where any other moneys are invested. Is $200K the entire portfolio? Don't know. I am in no way suggesting the OP to reveal details of his finances on a forum. I am just saying the whole picture should go into his thinking....and I am sure it does. You do want some equity exposure at age 68 (or at any age in my book).

Yes, ETFs are advantageous over mutual funds with the same basket of securities in that you can control the timing of your capital gains. This matters most if one is in a high tax bracket. It also an advantage when you die as your heirs get a stepped-up basis on the inherited assets.

Dollar-cost averaging does a nice job of reducing volatility.

A broad-based index fund or ETF(s) will almost certainly be up in 20 years and very likely be up in 10 years. No one can tell you if it will be up or down in 1 or 2 or 3 years. I know, everybody knows that.

Your investment time horizon does not necessarily have to end with your death. I have stocks including ETFs that I inherited from my mother and she has been gone a long time. I am sure I will pass securities to my heirs as well.

Get professional advisor
 

Get a professional advisor that is a licensed fiduciary rather than rely on misc. people from a a chat board. May cost a few bucks but will probably be well worth it.

I don't know what you mean by a licensed fiduciary. A fiduciary does not need a license.

“Get a professional advisor, it will only cost you a few bucks”! What’s a few bucks? I had a firm tell me it will cost me $60k a year for their help. Is that a few bucks? In 10 years, that’s over $600k, is that a few bucks? I knew what these people charge decades ago and that’s when I decided to do things myself.

I know for a fact I can do better than them, since a few firms call me every few months. I ask them can they do better than what I do and none of them will guarantee me that they can do better. I can prove what I make so it would be very easy to compare but they won’t tell me what their average return is for the year. I have helped friends with their investments and every one of them used a big brokerage firm to handle their investments and every 1 of them did poorly compared to the what could have been made with the better index funds and stocks.
I threw out a few mutual funds that are making 21-27%, compare them to what you are currently making in your brokerage managed investments. Then my index funds are making 35-40% and some stocks I have are making couple hundred %, how are these gains compared to what you are making?.then subtract their fees and loads.
Learn to do this yourself!

Pretty please, with a cherry on top this time... Specifically, which index funds?