Can a person learn critical thinking only using some texts, for example from textbooks? Or one needs interactive courses with video lectures, online exercises, and other things? I personally tried both methods and both can be used. But both have their vices and virtues. You can probably also find a course with a real tutor, for example via videoconferencing or even take a real class somewhere, it is similar to online courses but also have its specific sides.
Books are good if you have enough motivation to read them carefully, do exercises, and check yourself honestly. So if you need a teacher it may be a bad way for you. You may also need to do some research: check different web-site for related topics and check other books. If you like to work with texts it may be suitable for you. You also need to plan your education yourself: set deadlines and time frames when to do something. You probably can find yourself a company, but usually you are going to learn yourself, without any help or interference from peers.
Online courses may have a specific start date and end date, so you may need to plan your education accordingly. Sometimes you can find a course that can be started anytime, but it depends on a topic. Some sites with online courses also provide forums to discuss the syllabus and other related things. So you can communicate with other students, you can also decide how much communication do you want, for example you may just ignore such forums entirely.
Tutoring and having a real teacher is closer to online courses. You will have someone who may lecture you and check your work. You may have a specific schedule or if it is a personal tutoring, you may have flexible time frames. But most likely it will be the most expensive way to study. Would it be the most effective? I can’t promise that, some people accomplish more with self-study. You may also get a teacher who can’t understand you well enough to effectively teach you or you may have other issues with this person.
Most people have some experience with group classes at school, some have experience with private tutoring. You can try working on a textbook and start an online course, then you can compare and choose what is more effective for you.