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Well yes, but... Depends on what you mean. What do you mean?
Apk mirror is trust worthy in the sense that they do not tamper with the files and get them from gplay. Which aspect of the apk acquisition process do you find questionable? Though continually getting files from apkmirror is rather impractical and not the best method.
Antennapod is only available from gplay and fdroid. Where do you normally get your other apps from? Get it from there. If use use aurora/Gstore then from there, and if you use some fdroid app then get from there.
If you only have obtanium on your system then I see why you are facing this problem. If you wish to only stay with obtanium then Dumdum 's suggestion was probably the best suggestion.