It's not possible to do that in the new GUI, but the information is available via our dashboard API.
To use the API, first create an API token at https://my.opalstack.com/tokens/ and make a note of the token key.
After you have your token you can run the following command in a SSH session on your server to list your domains that have SPF records:
export TOKEN=YOUR_TOKEN_HERE
curl -s -H "Content-Type:application/json" -H "Authorization: Token $TOKEN" \
https://my.opalstack.com/api/v1/dnsrecord/list/?embed=domain | \
jq -r '.[] | select(.content | contains("v=spf")) | "\(.domain.name)\t\(.content)"' | sort