This is from lxqt 5.7.1 iso:
Boost.Python error in job "packages".
Command 'apt-get update' returned non-zero exit status 100.
Ign:1 http://security.debian.org testing/updates InRelease Err:2 http://security.debian.org testing/updates Release 404 Not Found [IP: 151.101.184.204 80] Hit:3 http://ftp.debian.org/debian testing InRelease Hit:4 https://sparkylinux.org/repo core InRelease Hit:5 https://sparkylinux.org/repo testing InRelease Reading package lists... E: The repository 'http://security.debian.org testing/updates Release' does not have a Release file.
Traceback:
File "/usr/lib/x86_64-linux-gnu/calamares/modules/packages/main.py", line 515, in run
pkgman.update_db()
File "/usr/lib/x86_64-linux-gnu/calamares/modules/packages/main.py", line 267, in update_db
check_target_env_call(["apt-get", "update"])
File "<string>", line 11, in <module>
Grab 5.8 RC ISO from here:
https://sourceforge.net/projects/sparkylinux/files/testing/
Or wait few more days for next Sparky release.
If you decide to go with 5.8 RC read this:
https://sparkylinux.org/sparky-5-transition/
Got the 5.8 RC as advised - still no luck.
https://ibb.co/f2Zh6q6
Will wait for the next release.
Unfortunately the 5.7.1 & 5.8 RC uses old Debian repos, which are not in use any more.
You can use Sparky Advanced installer which does not upgrade the package list, even uses old Debian's repo (if you do not try to install other desktop via Minimal ISO). So, if you install the system as it is, via the Advanced installer, the error you got, will not break your installation.
Anyway, new 5.8 iso images are on the way, should be ready next week.