Okay they might actually be variants
For what it's worth, Kanjipedia (maintained by the organization that runs the Kanji Kentei) has separate, non-overlapping entries for them, except to point out that they look similar and to be careful not to confuse them.
https://www.kanjipedia.jp/kanji/0002197100
https://www.kanjipedia.jp/kanji/0006433000
Were you able to find any other sources that they are variants?
I checked Kanjikai.
昂 has 昻 listed as a variant.
昴 on the other hand has 𣆻 listed as a variant.
But they are separate entries.
It seems that 昴 is actually the Pleiades star cluster and the Green Godess probably made a mistake. 昂 only has a meaning similar to 高 as far as I can see.
Not really related to the Pleiades meaning, but here's a short excerpt I found in one of my dictionaries:
昴」は「昂」と間違えられやすい。
1986年、マラソン競技で著名な男子選手が子供に「昴」と名付けようとしたところ、常用漢字でも人名用漢字でもなかったため、代わりに「昂」（81年に人名用漢字）で出生届を出すというニュースが話題となった。その後「昴」は90年に人名用漢字になっている。人名確認としては生まれた年から誤りを疑うこともある。
昴 木村昴（声優。1990～）
昂 根尾昂（野球選手。2000～）、則本昂大（野球選手。1990～）
I searched the web for a source on this story and found: https://www.ytv.co.jp/michiura/time/2018/10/post-4506.html
Therefore I think they should not be treated as variants.
Interesting story. I could also find "昂 has 昻 listed as a variant.
昴 on the other hand has 𣆻 listed as a variant" on other sites like https://kanji.jitenon.jp . All I really had to go off, was this entry https://imgur.com/a/OGErdEq , and it's also the only entry on this (at least from what I could find). But yes I agree, they don't seem to be variants.
Seems like an error then. I sent an email to Kenkyusha's editorial department to inquire. If they reply with anything I'll post it here.
Anything new?
Nothing on my end at least. Situation seems quite clear cut to me, maybe they didn't bother with answering. I can try again soon-ish though. Or maybe someone else can try. But ultimately this is akin to a little typo.
Yea I guessed as much. No need to inquire further imo, if they didnt respond first time. Thanks
昂 - 昴 ?
So 昴 is used to refer to the Pleiades star cluser a.o. , but I've just also found 昂 in it's stead. 昂 is listed as "The pleiades" in the GG5 (新和英大辞典 第５版), but nowhere else. Thought I'd post this here before proposing an edit in jmdict because I might be missing something here? As far as I know those 2 kanji don't seem to be variants of each other?