[DiapDealer]

Defender's random detection of Trojan:Win32/Wacatac.B!ml is like the smoke detector going off when you're cooking. It's typically heuristic nonsense. Especially when only one out of 100 or so anti-malware systems "detect" it. It's heuristics include "cloud reputation.". Which means that "not very many people have downloaded it" is one of the determining factors for flagging it as wacatac.b!ml.

For the record, whether you download Sigil's installer with links from its website, or directly from GitHub, or via Windows' built-in winget tool, the exact same file is being downloaded (directly from Sigil's github release page). Winget has the advantage of avoiding the unsafe, unknown, uncommon download warnings that Microsoft throws at users to scare them into not using software that hasn't paid the ransom to "maybe" get off the "heuristically possible to be" naughty list. Winget vets installers before accepting them. As does Chocolatey. So you tend to get safe, silent installations of Sigil with them.