Runestones in both the real world, like
- Elder Futhark, where "Alföðr" (Allfather, Odin) is written as ᚨᛚᚠᛁᛟᚦᚱ
- Younger Futhark, where it is written as ᛅᛚᚠᛁᚬᚦᛦ instead.
Valheim uses Elder Futhark, which was used BEFORE the viking age began in the 9th century. Most runestones from that time use Younger Futhark.
Elder Furthark eventually evolved into Younger Futhark as Proto-Norse evolved into Old Norse. Curiously, Younger Futhark has less runes than Elder Futhark, despite Old Norse being more complex than it's predecessor.
This means that either, Elder Futhark was chosen because it has more "letters" to represent what is written…
…or the runestones in Valheim are much older, placed there by people from as early as the 2nd century AD (which is the time period the first Elder Futhark runestones are from).
Make of that what you will, but I found it very interesting.
Source: The internet and my own curiosity.