An interesting bit from the linked ElcomSoft article:

>Brute force attacks became not just faster, but much smarter as well. The user’s existing passwords are an excellent starting point. These passwords can be pulled from the user’s Google Account, macOS, iOS or iCloud keychain, Microsoft Account, or simply extracted from the user’s computer. The user’s existing passwords give a hint at what character groups are likely used:

So if the victim used portions of that "longer than 20 characters" password in their other passwords, the amount of work required to crack the LUKS password would be much reduced.