Sadly, no. Mimestream already uses SwiftUI for parts of the UI, and SwiftUI requires Catalina. I plan to release an iOS/iPadOS version in the future, so Mimestream will be investing even more heavily into SwiftUI. At some point later this year, Big Sur will become a requirement, too. I sympathize with those that remain on Mojave, especially those who need to run 32-bit apps, but as a 1-man project, it seemed like a necessary tradeoff to make.