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.
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?