Before I get into the details of the error, and why it is happening - here is the best way to fix this Shopify inventory error: Go to all your past orders, and make sure they are marked as "fulfilled". If an older order is not fulfilled, it sometimes shows up in the inventory in the "committed" state. This is a huge problem, as it then changes all the other states - available, especially.
What is this inventory error: Recently, around Feb 2023, a few stores started noticing that their inventory is wrong on the Shopify admin, no matter how they update it. This has resulted in them doing weekly inventories now - because the errors are happening too often. And, even if you are not using Shopify POS, but are updating inventories manually - it can still result in this error. The error also could occur if you transfer inventores from one location to another location.
Why is the inventory error happening: This could be because of a new feature that Shopify introduced, which is affecting the way the system counts inventories.