Tldr: Not everything needs to be academic or literary. It is okay to read or converse for fun and not serious discussion. Think about things in context before making any judgment calls.

I think that a lot of people do not construct their online comments with proper reasoning and support in general and it is not related to booktok or booktube. Those people either don't care to support their statements or they never learned how to.

Additionally, I think that before we form any kind of statement on booktok or booktube, we should first consider the purpose and audience of that content. A lot (not all, but a lot) of the people engaging in booktube discourse are not actually interested in any literary analysis or review. It is more about books for escapism or smut. Sure, a book might have been an absolute mess in plot and pacing, but booktube betty still enjoyed the ride! They just want to talk about their opinion without considering the book through any particular lens.

And that's okay!

There is nothing wrong with liking books for those reasons or having conversations about them.

When I write reviews or recommendations, I nearly always start with "If you are looking for something that...." or "If you like x, then..." because a sweeping statement really won't be that helpful to a reader. You gotta put things in context as both a reader and a writer.

As for your own critical thinking skills, here is my advice.

First, decide WHY you are reading a book. Personally, I read at least 2 books at a time. One is an ebook for fun and that other is a physical book that I read for literary value.

Next, try to keep you brain engaged while reading. While I read both of these books, I am actively asking questions of the story and characters, making predictions of what will happen next, noting the author's word choices etc. But I am focusing on different things. As for my fun book, I am guaging how and what in the book is giving me enjoyment and it is okay for me to lose myself in it tbh. For literature, I am anotating how the author uses various tools to craft the story.