> Solus is a built from scratch distro. Sooo... Yes, no and maybe.
"package manager, eopkg, is based on the PiSi package management system from Pardus Linux,[3] and it has a semi-rolling release model, with new package updates landing in the stable repository every Friday"
"Solus is considered a curated rolling release. It is a rolling release in the sense that once installed, end-users are guaranteed to continuously receive security and software updates for their Solus installation"
I cannot yet find the main website for solus: but it is not a BSD, or LFS or TBLD or Buildroot something built from scratch.
Apparently end users can build (not without failures) packages available for re-build through it's package manager. The GITHUB link leads to some advertising website with no reference to any linux distro. The GITHUB has a ton of folders and which one would use to "get solus" is unlcear. While saying it is not a bleeding edge linux: there appears to be a focus on getting "Steam games" to run "better".
It has "interactions" with GIT and ubuntu snap - it's unlear if you "require ubuntu to install solus", ie, if it's another ubuntu based distro like the iconic "Mint" is, or not. Cannot find "what to download". Google says there is an image to put on USB i finally see.
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Do you run systemd? It is (endlessly) configurable as to "what is and isn't done at boot then after boot. I might as well not start describing it.
As for linux kernel: that's the problem with huge "all module all built-in" kernels. They can freeze on some platforms trying to load. Even if they don't - every module loaded (not needed) wastes takes times - possibly a frustrating wait.
I think Ubu has "fast booting" probably due to loading only modules needed to boot, putting others in background that were detected* and needed but not for gui desktop, which it probably manages (which to load which the PC doesn't have).
Ubu uses UDEV I think, which "should tell it what modules to load" (are present). Optionally one could defer some modules of a group unless an application that uses them is actually opened. Or like Win10 preload apps so they appear to open quickly

Fast is something strange since it can be slower.
As far as "fast boot", that's been in Windows and Linux for some time. There are also ways to:
1) load linux quicker without a bootloader (linux can be loaded directly into memory using certain bios options if kernel is built that way)
2) have linux loaded from bios memory automatically skipping part of all the available boot disk checking
fast ... depends on what you mean by fast