Porto to Sintra logistics

Of course there are many other possibilities, but if the goal is just to get to Sintra, the train is the way to go.

By train, you would change trains at Lisbon Oriente station when coming from Porto.

If you are going to central Lisbon after Sintra, you would then take a different line to Lisbon Rossio.
There is also a direct bus from Porto to Sintra that I believe someone on this forum may have once recommended or discussed.

I'm not having much luck finding train options between the 2. Checked April 2nd and closer dates in case that date is too far out. Cp.tp, TrainLine, even RailEurope. Seat 61, too.

April is too far away. I looked for options at cp.pt a random day in January and found a lot of them.

Yes, plenty of train options between Porto and Sintra with a change at Oriente. I'm sure there will be a few months before departure.

There also appears to be a direct bus that again can't be purchased yet. The bus is probably easier though I usually prefer trains to buses given the choice. My preference. The bus might be a little cheap I guess.

When I was there in 2019 taxis were not expensive and Uber was even less. The simplest, easiest way is to take taxi or uber from Oriente station to your hotel. The train from Oriente is slow and then it's an uncomfortable walk from the Sintra train station to the historic center along a mostly cobbled walk - not so easy with wheeled luggage. It will be faster and more comfortable than continuing by train and not much more money unless rates have gone up considerably.

I like trains and would greatly prefer one to a taxi in most cases. The train to Sintra worked fine for me. In any case, she is coming from Porto, so she's got to take a bus or train anyway most likely just to get down there.

I don't think I was doing anything different, but I tried some Dec. and Jan. dates on:
https://www.cp.pt/passageiros/en
again, and was able to get evidence that trains do indeed run from Porto/Lisbon/Sintra. No idea why the site was telling me nothing was available on previous tries.

Yes, you can do the train to Lisbon then another train to Sintra. However, I recently tried the express bus service from Cascais to Porto - then back again. It makes a stop both ways in Sintra also. The entire trip is four hours from Cascais so 30 minutes (approx.) less from Sintra.

It was great! So much easier than taking the train then taxi or metro to the station in Lisbon before getting on the train to Porto. It was also cheaper, even though the trains are very inexpensive. It’s just very nice to get on one bus all the way without making a change. I will likely always do the bus from now on. The company is Gypsyy. It’s easy to google and purchase tickets ahead of time, too.