On my computer, I go to disneyplus.com, click on the “Disney” tab, look on the 2nd row of the listings under “Walt Disney Animation Studio”. There is the original Fantasia as well as Fantasia 2000. I just finished the original version & just started the 2000 version. So far, it’s NOT as good as the original, but not that bad either!!! I did see 101 Dalmatians listed but didn’t see Lady & the Tramp; so I found the “Search” tab & typed in “Lady” & boom, there it was. On the “WD Animation Studio” row, I also found Cinderella, Snow White, The Little Mermaid, The Jungle Book, Beauty & The Beast, Frozen, Frozen II, The Princess & the Frog, Sleeping Beauty, The Fox & The Hound, Alice In Wonderland, The Lion King.
Like @SEKA I use Roku to access my streaming stuff & I had to do a Roku Search in order to find them on my TV. After searching Disney+ on my computer, when I went back to my Roku, they had ALL magically appeared on my TV!!! Again, I just clicked on the “Disney” tab & the first row under it was “Originals” & the 2nd row was “Walt Disney Animation Studio”. Most of the good old stuff is on that row. The 3rd row marked “Additional Animated Movies” has some of the pretty good newer stuff like the #2 versions of the originals. The very bottom row is “Vintage Disney” which as some of ones that I like, but not sure that you’ll enjoy them!!!
Not sure how you watch, but this should give you some ideas of what you’ll find. The search bar is your best bet, but learning how they break them down by subject will also help.
Thanks for asking this Q as you gave me a reason to explore my recently acquired purchase & now I have my weekend scheduled full of Disney…most of which take me back to the “good old days”!!!