Yes, you can buy crypto using the Blockfolio app. Previously, Blockfolio only offered portfolio tracking, but following their acquisition by FTX in 2020, they started offering in-app trading via FTX.COM and FTX.US.
Technically speaking, the Blockfolio site notes that "Blockfolio does not provide trading services. Trading services offered through the Blockfolio site are provided by FTX.US for U.S. residents only, and FTX.COM for all other regions." You won't find much information on the website, nor are the features accessible via desktop. Instead, users must download the iOS or Android app.