just tried to install on Windows 10 but Windows defender flag it as malware
It shouldn't. Are you sure it is the Defender (anti-malware net firewall) and not the DEP (data execution prevention) service? Matter is, v3.4.10 used to load the scripts and the machine code precompiled by the Asm jitter into the data, not executable code, memory which is what many simpler virus writing strategies would do. The restrictive DEP service that's initially switched on in clean MS Windows installations would avoid code execution in such memory areas and flag the respective executables as potentially dangerous, which FBSL of course isn't. FBSL v3.5 works differently and avoids that restriction.
I'd suggest switching off the DEP service when working with FBSL v3.4.10 on the latest MS Windows platforms. I think my complete personal authenticity as a member of this forum is a solid guarantee that noone here means harm to your computer, at least as far as FBSL is concerned.