我用几个网站、APP、视频和中国的电视节目来帮助我学习。

I added '帮助我学习' because in this sentence you stated that you use sites, apps, and videos, but you don't say what you are using them for. Even though you stated you are self-learning Chinese in your first sentence, this doesn't carry over to the next one. The correction shows that you are using these materials to help you learn, helping the reader know the purpose of you using these things.

我试过学中文一共三次一共试过三次学(习)中文。

Your original sentence was a '病句', which is the equivalent of getting all the content right, but in the wrong order. Seeing as you are an English native, I believe you tried to directly translate your phrase from the sentence "I tried to learn Chinese a total of three times", however this doesn't make sense in your order. Instead, if you write '我一共试过三次学习中文', this shows you tried to learn Chinese three times, and also implies you picked it back up three times after giving up, in a sense. '学习' sounds more right in my opinion, but grammatically, it doesn't really matter.

我第一次学习中文是在2014年，我学了半年。

第二次学习是在2021年，我又学了半年。

现在是我的第三次，我从2025年一月开始学中文。

尽管有困难，我还是喜欢学中文，因为我喜欢一个挑战自己/接受挑战。

After '还' you should add a '是' for clarity. Since you didn't, although I could understand the meaning of your sentence, it made it rather awkward to read. When you wrote '一个挑战' I am assuming you mean that you 'like a challenge', however this does not translate properly in Chinese in your context. It would mean something along the lines of 'I like one challenge'. Instead, I put in two options that are clearer. The first means you enjoy challenging yourself [with the task of learning Chinese], while the second means you like to accept challenges.

尽管有困难，我还喜欢学中文，因为我喜欢一个挑战。

我用通过几个网站、APP、视频和中国的电视节目学习。

尽管有困难，我还是喜欢学中文，因为我喜欢一个挑战。

还是 = still.