I will look into Armstrong Redwoods. The Giants game is at night, so we do have most of the day; however, there are a few places in SF we’d like to visit, too.
Sure. I just hesitate to recommend Muir Woods these days. It's kind of the bottom of my list of any place I'd recommend to see old growth redwoods, but the places I recommend are further away from San Francisco. Muir Woods is basically what's left of old growth redwoods within maybe 25 miles of San Francisco (due to timber cutting to rebuild after the 1906 Earthquake) and I mentioned the crowds. The tallest redwood there is about 250 feet tall, but up the north coast of California it's easy to find trees that are over 300 feet tall (possibly 350 feet) and much wider. I used to go there a lot, but it just doesn't seem as impressive any more after finally seeing redwoods further north around Eureka and Crescent City.
There is a small set of old growth redwoods in Marin County where no reservation is needed. There is a parking fee though, but no entrance fee. I used to drive by the area when I went to Point Reyes National Seashore.
https://www.redwoodhikes.com/Taylor/Pioneer.html
That being said, I looked at the reservation system and at least this week it's not so bad. Not sure what it's going to be like during the peak summer season, but I could get a parking reservation for tomorrow and this weekend at any time. Reservations are available 3 calendar months in advance for $9.50 per car. If you're really looking to do it, I'd think you shouldn't have too much problem getting a reservation if you get it early. The other thing is that they now have a $15 per adult (16+) entrance fee and a $45 annual pass (allows up to 4 adults). Then there's the $80 federal lands pass, which can make sense if you're visiting other areas (mostly national parks) in the next 12 months.
This is the official website for the reservations provider and the entrance fee information.
https://gomuirwoods.com/muir/buy
https://www.nps.gov/muwo/planyourvisit/reservations.htm
https://www.nps.gov/planyourvisit/passes.htm
Have fun. I know I'm kind of a downer about Muir Woods, but it's kind of been loved to death. When I was finally able to visit Redwood National Park, Muir Woods just wasn't as nice. for various reasons including crowds and the overall experience.
There are other areas too, such as in San Mateo County. This is a pretty good resource.
https://www.redwoodhikes.com
There are some really nice redwood groves more than 50 miles south of San Francisco, so distance might be a deterrent. The advantage of going south would be that you don't need to worry about bridge toll on the Golden Gate Bridge.
This one doesn't seem to bad - a county park in San Mateo County. But it's not easy to get to and almost on the border with Santa Cruz County. Most of the redwoods aren't going to be old growth, but they have some left.
https://www.smcgov.org/parks/sam-mcdonald-park-natural-features