The equation holds and is in fact super straight forward (one might say trivial) to prove from alternative algebra.
To avoid confusion, the amendment equation reads:
(𝑥𝑥*)𝑦−𝑥(𝑥*𝑦)=(𝑦𝑥)𝑥*−𝑦(𝑥𝑥*)
However, this follows immediately from the fact that in any alternative algebra 𝔸 and 𝑎,𝑏,𝑐∈𝔸 it holds:
(𝑎𝑏)𝑐−𝑎(𝑏𝑐)=(𝑐𝑎)𝑏−𝑐(𝑎𝑏)
or using the associator:
[𝑎,𝑏,𝑐]=[𝑐,𝑎,𝑏]
since
[𝑎,𝑏,𝑐]=−[𝑎,𝑐,𝑏]=[𝑐,𝑎,𝑏]
See for example https://en.wikipedia.org/wiki/Alternative_algebra#The_associator
Thus, since the octonions and the bioctonions are alternative, your amendment is correct by setting 𝑎=𝑥,𝑏=𝑥*,𝑐=𝑦.
PS: John Carlos Baez (npub1nf4…nqe4) either you edited your post, or more likely my phone did not render the maths correctly. Now on my computer it look the same 👍