I was looking for a crawled property for the list item / document version - stumbled on a few such as _Version, Version, Version0, ows_DocVersion. I have mapped them to the tenant's RefineableDecimal00.
Of course, I have re-indexed the site collection.
However, when making a search query for the property, it returns an empty value.
For example, here is a test KQL I am using in the Chrome SP Editor -> PnP JS Console:
Posting our solution as somebody else might find it useful:
1. We mapped the UI Version property (ows_q_TEXT__UIVersionString) to one of the Refinable Decimals
2. We have given the refinable decimal an alias (SharePointVersion) in our case.
So we were able to sort, and filter via a KQL the results, i.e. SharePointVersion>=2.1 was giving us items with version greater than or equal to 2.1 - it seems that SharePoint have successfully managed to parse the decimal value into the decimal property.