Can you learn to read and write in any language using an online site like Duolingo?

After using Duolingo every day for over two years, I’d say that I can read some, picking up some words here and there, but not write Spanish very well. I went to Mexico 2 years ago when I had just started Duolingo, and I was tongue-tied. I just returned from my next trip, and this time I was able to say a few words, not in fluid sentences, but words here and there that were enough for the native speaker to get the gist of what I was getting at…nothing difficult, however. The free Duolingo version has a 5 heart (mistake) per day limitation, which one exhausts easily. The paid Duolingo version has no heart limitation, but in my experience, I’ve been besieged with considerable program slowdowns of a variety of types: screen freezes, audio arriving late, audio cutting out, etc. up until the last few days, and I’ve been using it for six months. IMO, I don’t believe that one can learn to read and write in any language using an online site like Duolingo. However, at least some of the competing programs have “lifetime” options that one can purchase through places like Stack Social, and they don’t seem to have the technical problems that Duolingo has.