Museum pass for Versailles

https://en.chateauversailles.fr/plan-your-visit/conditions-free-admission#free-admission

This is directly from the website:

The Paris Museum Pass grants admission to the Palace of Versailles, the Estate of Trianon and more than 60 museums and monuments in Paris and the Paris region.

In order to access to the Palace of Versailles with the Paris Museum Pass, you need to book a free timed entry "Palace Ticket" online.
It does not grant admission to the Gardens on Musical Fountains show and Musical Gardens.

Related question (forgive me, it is our first trip to Paris). Can we get the timed entry ticket once we arrive in Paris, or do we need to book in advance before we leave the states? How difficult its it to schedule timed entry? We have 1 day to do Versailles

You can probably get a slot a few days in advance BUT if you know your day I would nail it down. We have several times been surprised that museums we used to schedule a day in advance required longer now. And Versailles is a very busy place and with little wiggle room, you should nail down your time. If you want to go on a Fountain day get a chateau entry mid day as the fountains run in the morning and afternoon. You cannot re-enter the palace, but you can re-enter the gardens on your ticket.

And if you want to go to the fountains, I think I remember an option to pay for just that as an add on to your admission with the pass. We went to Les Grand Eaux Nocturne.

If you are planning to visit the gardens and the Estate of Trianon, make sure to book a Passport ticket, not just a ticket for the palace. I followed the instructions on the PMP site and just booked a Palace ticket, and almost panicked when we were there recently that I wasn't going to be able to visit Trianon. Fortunately, I think they just scanned the PMP at Trianon so it wasn't a big deal, but if you are going at a busier time it might be.

If you know what day you are going I would book a timed ticket for early morning. The early morning tickets do sell out and, in fact, we booked ours several weeks in advance and didn't get the first time slot like we wanted. We did get tickets for an hour after opening and got in without a wait. We were able to walk through the palace pretty easily with minimal crowds and then had the rest of the day to do the gardens which are magnificent. It should be noted that when we existed the palace the lines were insanely long.

We used Rick's audio tour and it was very helpful.

Enjoy your trip!