Well, it depends. Some apps offer free comics for a limited time or have a selection of free titles. Comixology and Manga Rock are examples, but be cautious of ads and potential copyright issues.
Lezhin Comics are not free in general. You have to spend money to enjoy the majority of their comics. But sometimes, they might offer free chapters or special deals for new users or during certain events.
Lehzin Comics has a mix of free and paid content. Usually, popular and newly released comics are behind a paywall, while a few older or less popular ones might be free to read.
Pixton Comics has a free version available with certain limitations. To unlock all the features and get the most out of it, you may have to pay. But the free version still allows for a decent amount of creativity and comic-making.