There is currently no way to create an account for the bug tracker.
I'm not reporting this because of needing to create another account for myself, but because someone who wanted to report a crash can't create an account to do so and there's no instructions on how to proceed then.
There may also be more people willing to do so, or to vote for bugs. Instructions on an alternative way to report those or more information about the issue would be useful.
I am aware account creation being closed is currently intended (for a reason I don't know, but found 2 month old bugs about it), but there's no documentation about it/about why, no alternative to report issues without previously having an account and documentation still tells you to create an account normally while linking to an error page.
Currently, as you said, there is no way to create a Mojira account
However, if you ask it in Mojira discord, for example, you can find a better place to ask for a solution, or have someone else report it for you, or check for duplicates or if it is a valid bug.