This happened to me on my iPhone 8, and I didn’t have AppleCare (first time ever, go figure) and tried a number of measures to keep the cracking from getting worse: tape, a glass screen protecto, a Zagg-type screen protector inside an otterbox case, etc. and I STILL had major ongoing cracking issues.
I ended up biting the bullet and doing a full handset replacement, which was about $349 through Apple.