To gain more readers there are different things
Mirror your content, post your series in many sites/apps as possible, check out where you can post your webcomics or novels. If you can translate it to other languages, Webtoon and Tapas aren't the only platforms out there.
Promoting on several platforms such as Discord Servers, Facebook groups, SubReddits, Twitter, Instagram, Forums, etc.
Something I see is that (Especially writers) authors, instead of building a proper posting schedule to allow new readers to adapt to the content, to make the algorithm have a steady flow; they just dump their entire series expecting people will get interested like that, when the reality is no. Another thing that annoys readers or even other creators who are subscribed to other's stories and especially on Tapas is notifications of authors constantly editing the chapters several times and well, not knowing when exactly does an author updates.
Fanbases aren't build in thin air just because you've been posting your series for a few months, no, it takes years even more than 1 or 2, and several authors originally start with less popular, even shorter, series, some even change accounts so much that followers cannot keep track of then, as well, the most important thing is to make things accesible for readers, you're asking way too much even if you believe it's not, most of people only care about scrolling and see the next post of the content they see, so you either have to make extremely catchy stuff so they click the link to your series or chapter or be more creative with promo art, chapter previews and such.
Sadly, for most of authors that are not popular, what I've seen that boost their flow is for them to become content creators, not just mere writers or artists. Basically overwork yourself with challenges, art studies, tutorials, art classes, fanarts, tips, vlogs, streaming, speedpaintings, original art, fancomics, NSFW, memes, animations, promotional art, reading sessions (Of other people's content), constant engagement with other people be it fellow creators, those who aspire to be creators or just readers. And all of the above on different formats for several platforms, be it TikTok, Youtube, Twitch, Twitter, Instagram, etc.