I had the same issue with a new SSL certificate renewed on ssls.com

Our app no longer functions on Android 13 when REST API requests are in use, and embedded browsing is also broken.

I managed to solve it by contacting ssls.com support and they told me to start renewing the certificate, but don't enter the verification code in Sectigo's form. Meanwhile they contacted Sectigo and they provided files with a correct ca-bundle file in it. Then I finished the verification as usual, got the Zip file with the certificate files and created the PFX file from them, also embedding the ca-bundle file via openssl command line. (This was a new step for me.

With this fixed certificate (and bundle) everything works on Android 13 and earlier versions. Let's hope they will fix this issue soon on Sectigo's end, but at least there is a workaround that Support may be able to provide.