You can remove the /usr/local/cpanel/base/frontend/jupiter directory on your server to get rid of Jupiter. I would probably recommend tarring up the directory first, so you have a backup copy of it.
tar -cf /root/jupiter.tar /usr/local/cpanel/base/frontend/jupiter
rm -rf /usr/local/cpanel/base/frontend/jupiter
(of note: always be careful when using rm -rf You should be knowing exactly what you're doing anytime you rm -rf something)
You will also need to set the ng-cpanel-jupiter-apps package to unmanaged
/usr/local/cpanel/scripts/update_local_rpm_versions --edit target_settings.ng-cpanel-jupiter-apps unmanaged
If you have automatic updates enabled, you'll probably have to do all of this every day, after each nightly automatic update.
If you don't have automatic updates enabled, then you'll probably have to do this every time you issue an update.
A lot of this push to switch to Jupiter reeks of cPanel wanting to announce that they're still developing their product. The tried and true axiom of: "if it an't broke, we'll fix it!"
I remember - probably a decade or two ago - when cPanel offered multiple themes. I forget what they were all called. But from an administration point of view, it was a nightmare. If you wanted to modify or add something to the end-user's cPanel you had to modify it for every single theme. And what was the point? It's not like end users log into their cPanel every day to admire how pretty it looks. I stated as much back then. Functionality is the key to a cPanel interface - and for probably 98% of end users, as long as they can log into their cPanel and create an email account, that's all they need.
To advocate on the cPanel side of things for a bit, sure maybe you want to steer the product into a different direction and integrated those changes into an old theme (paper_lantern) might be overwhelming. Creating a new theme (Jupiter) from scratch might be the best way to go. But for those of us (maybe just me?) who prefer stability over bleeding edge, sure announcing that the old theme (paper_lantern) will be removed in upcoming versions is warranted. And I can certainly appreciate the need to make this well known.
While I can't speak for everyone, but for me - job accomplished. I'm fully aware that paper_lantern will be removed in cPanel 108. I'm not using cPanel 108. I don't have any plans to move to cPanel 108 until I have to. I tend to stick to TLS versions. I'm assuming given all of the fan fare, that cPanel 108 will likely be the next TLS release. But that likely won't happen until some time in 2023. I don't need bright pop up notifications in my reseller's WHMs telling them to switch to Jupiter "RIGHT NOW!!!!!!!" I will decide when to tell my resellers that they need to switch to Jupiter.