Chromium validates website TLS certificates by default. Uploaded custom certificate authorities and certificate CRUD endpoints are not available in the native browser API.
A supported transport may accept browserSettings.ignoreCertificateErrors:true at creation for a deliberate controlled test. That changes website certificate checks inside that session; it does not change Tooluse.net API TLS validation or install a trusted authority. Prefer valid certificates for normal browsing.
See Create a browser session and the Browsers API for authentication, request fields, and limits.