Not sure if you're in the US, but in the US the second you publish either physically or digitally, your story is copyrighted, you don't need to apply for any protections under the law, you just get it by default. Trademarks apply to logos and designs and copyrights apply to stories (in the US). You can't trademark a story but you can trademark characteristic designs that you might use for marketing.
Again, maybe you aren't in the US and your laws work differently, but if you are in the US, then I'm not actually sure you're doing anything that actually helps yourself, unless you've already got some established universe with characters that are going to sell merchandise the second your story publishes, and even then anyone trying to use your IP would still have to make it "legally distinct".
Edit: This isn't legal advice, just musings on the function of copyright vs trademarks.
We've seen a good example of the two recently with Steamboat Willie and the Disney Logo. The Disney Logo is a trademark, and can be renewed in perpetuity, where as the Steamboat Willie character and story are copyrighted and have recently entered public domain. You can't use a certain outline of Steamboat Willie because it's the disney trademark, but you can do whatever you want now with the character himself. Likewise, prior to this you couldn't sell your own Steamboat Willie figurines because of the copyright. Now, hypothetically, you can, as long as your tiptoe around any other disney trademarks and copyright, but damn it would be hard.
Additionally, registering a trademark costs hundreds of dollars and takes nearly a year to be processed. If you're a publishing author with some LLC that you publish through, it'd be worth it to register a few trademarks related to your business and pseudonyms or series titles, but if you're just starting out with a webnovel, you'll be completely protected for most cases under copyright law. The reason you'd even want the trademark is mostly to allow you to more aggressively pursue lawsuits of infringement of your business, which to do in any effective regards would require you to keep a lawyer on retainer, unless you just plan on bluffing by having ChatGPT draft a cease and desist letter and never actually follow through on your lawsuit if the recipient doesn't actually comply.
