Online SRD vs Official PDF SRD

The question I have is pretty simple. The PDF file that WotC has on their website does not have the same content as this website https://www.5esrd.com/.

If I create a 5e adventure and want to go the OGL route instead of the DMs Guild one, can I use the extra content from the website?

As an example, the website contains a creature named Witchlight. The creature is from the Tome of Beasts, which is a Kobold Press release. What are the restrains there, if any? Reading the title of the website, as it contains SRD in it, it makes me think that I can. But the confusion arises when I don’t see the same content in the WotC file. Can I use this creature and any other that is not in the PDF of WotC?

Thank you all in advance.