This fell out of a conversation with Eli Zaretskii on reddit.

report-emacs-bug has methods to attempt to send the bug via email, but
this does not work well for users who do have not configured either
Emacs or an installed email client on their computer. Accessing email
via webmail has become very popular, and users who do so probably have
never even looked for their server settings, so they'd have problems
setting it up.

I think we could provide these users a better user
experience. Currently, when trying to send the bug, if email is not set
up, Emacs presents three options: mail client, transport, and smtp. We
could add a fourth option, "send manually", where this option copies the
body of the text to the system clipboard, so the user could switch to
their browser and paste it. The command could even allow the user to
come back, press RET, then copy the subject, and a third time for the
address to send to.

It's not quite as nice as being able to directly send the email, but I
think this or something like it would be a better experience for people
who do not have their system configured to send email.