Why Sololearn does not have frameworks courses ?

Answer 1

They do have framework courses.

Angular + nestjs (requires pro): https://www.sololearn.com/Course/fullstack/
Bootstrap3 : https://www.sololearn.com/learn/1051/

React is listed as [coming soon]. If you have a specific framework or two in mind. Send feedback as suggested.

Answer 2

Send feedback on [e-mail]