You may have started seeing this error on Google Search Console. This is starting to be a common problem with pages that are not yet indexed or newly indexed.
This problem, which appears at the bottom after inspecting the URL in the GSC panel, appears in interface as “It may prevent the page from being indexed because HTTPS is not valid”.
Determining the Size of the Problem
If this error is reflected on the screen on all your pages, including your homepage, the problem is with your SSL certificate. You should definitely test it. You can quickly view your certificate details from the green lock button on the browser bar. If there is a problem with your certificate afterward, you need to update it.
This is normal if the problem is only with new content that has not entered the index. Over time, Google will index your content/page and remove this warning. There is nothing to worry about.