Cydia Impactor is unusable now and we won't know if it ever will get updated. You will always be relying on 3rd party signing services that continually get revoked if you want to stay on unc0ver. You can use checkra1n on 12.4. That is what I am on until my tweaks are updated to ios13. Use batchomatic to create online.deb to save all of your tweaks. Then remove unc0ver in it's settings gear by choosing root fs. Your phone will reboot and be un-jailbroken. Then download checkra1n 9.5, open it and then plug in your phone, follow the steps and once it jailbreaks, install Cydia, download filza, download batchomatic. your .deb will be in Filza, tap install and then run batchomatic. All of your tweaks will load back to Cyida. That's it. Never have to sign checkra1n or use ReProvison. Staying on 12.4 gives you the option to use checkra1n or unc0ver. Personally checkra1n is very stable on my 7+ on 12.4 and has never rebooted.