What makes a back link "Potentially Toxic"?

Hi everyone,

I created some websites and linked back to my own website in the footer credit. I'm just dabbling in SEMrush and using its backlink audit tool. It shows the website that I created is potentially toxic. Is this something common that I could ignore? Why would SEMrush mark the site I built toxic? It is a fully static website and no weird information. Thanks for your help.