I was able to reproduce this with Windows 11 and the Gentium Plus 6.200 fonts on my laptop.
https://software.sil.org/gentium/download/
Here are the steps:
- Download the Gentium fonts und unzip them.
- Right-click the Desktop, select Display Settings or enter Display Settings in the Search box.
- Scroll down to Scale & layout, select Custom Scaling and enter 120.
- Windows will ask you to log out.
- Login again and create a blank epub2 oder epub3 book.
- Add woff or woff2 fonts from the web sub folder to the Sigil Fonts folder.
BTW, Sigil won't crash, if any of the Gentium .ttf fonts are added to the Fonts folder. while custom scaling is in effect. It also appears that the Sigil font handler
might have problems reading the font metadata, because it displays "No reliable font data" instead of the font name for all woff and woff2 fonts when no custom scaling is in effect.