I had 2 mojang accounts for my kids, attached to 2 separate Java game licenses (because i couldn't buy 2 licenses for 1 account) used on Linux. When Microsoft forced the authentication conversion, I had to disassociate 1 of the 2 emails from the combined MS account (that I had worked really hard to combine in 2020) reincarnate that email as a separate MS account, associate it with the separate Mojang account (because MS also has no way of supporting 2 licenses on 1 MS account, even if the account listed multiple emails) and then I was promptly banned by Microsoft for breach of TOS, whatever that might have been. 12 hours later and a dozen support contacts to Mojang, I was unbanned... but my kids didn't play Minecraft that day.
To any MS/Mojang folks lurking,- great game but the authentication merge was an unforced error.