For some reason Synfig 1.5.5 running as appimage on my Linux Mint doesn’t feel as fast as 1.5.3 running installed by software manager or flathub.org. I tested zooming in/out in navigator window and it is very choppy when running appimage version.
Is there a possibility there will be an installer for v1.5.5 on Linux?
Official AppImage are built on a set of (quite old) GTK 3.22 and other libs packages all together, while distro packages and flatpaks are built according the libs available on the distro and on the updated libs from flatpak system.
For an installer version, you should contact the distro’s maintainer (apt info synfigstudio, line starting with Maintainer:)
For flatpak, we could summon @ice0 for apply his magic on the configuration of the flatpak config files
In the meantime, you could simply clone the repo, install the deps and compile it, it’s straightforward and have access to the latests modifications.
(Note: my UNOFFICIAL builds still use the same libs as the official ones, so in your case they shouldn’t solve your issue of display)
I read some status with migration issues for Synfig 1.5.5 here for debian (ubuntu, linux mint): synfig - Debian Package Tracker
As you can see, the blocking for update in the packages is that they failed to compile for i386 and s390x.
So it is not published.
Who will still use a i386 and who would be using Synfig on an IBM Mainframe? Mistery!
But as it is the policy of Debian, it is blocked (either it works everywhere or it is not updated).
So better to use alternatives than wait for as I guess your CPU is not so “exotic”.
Or to compile it yourself.
Note that you could even create your own .deb with CMake script, but this would be limited to your current OS distro (cpu/bitness/os version) as we had the case for the AppImage by @zainal (see here)
I often build Synfig myself on Linux. A full build usually takes around 11 minutes. If I only make changes to the core, an incremental rebuild is much faster—usually less than a minute.
How long does it typically take to build the Synfig AppImage?
About the same time for me with morevna-builds.
It also depends on the machine (cpu/core/ram/ssd speed) and the number of threads allowed during the compilation.
But even an asthmatic turtle should be able to do it in less than 30 minutes
I tried building 1.5.5 from source and the “autotools” build runs better than the “cmake” build in terms of time it takes to open/loading project scenes and using the preview rendering or using “Render future and past frames…” enabled. Its a big difference in speed.
Anyway, now synfig runs really smooth like the 1.5.3 installer on Linux mint (thanks to building with autotools).
It should be the same at execution unless debug is activated.
And for compilation time, it’s the number of threads.
I used the “2-build-production.sh” script for the autotools build. For Cmake I used default build config as in the steps provided in build manual. Synfig still runs best on the autotools build, its weird…
For CMake, you should use 2-build-cmake.sh (by default it is in Release mode when no parameter is added).
In the Manual instructions, the output is ./output/Debug/bin/synfigstudio, I think that there is where is the difference 
P.S.: Don’t forget to delete cmake-build folder before restarting the compilation otherwise it may use some cached version
