Google.com Root certificate showing as not trusted (Man in the middle attack?)

I get the alarming message above on both my iPhone and iPad, despite trying both the bootstrapped NextDNS config file and the low Latency App Store app. Granted it’s a third party app but it’s  still confusing because I have experienced some hacking in the past and I didn’t think this would occur with  a secure service like NextDNS. Can anyone help or clarify this for me?