Power Query M code
let
Source = YourTable,
AddedDateTime = Table.AddColumn(Source, "ConvertedDateTime", each #datetime(1970, 1, 1, 0, 0, 0) + #duration(0, 0, 0, [UnixTimestamp]), type datetime)
in
AddedDateTime
Converts a Unix epoch timestamp (seconds since 1970-01-01) into a proper DateTime value.
let
Source = YourTable,
AddedDateTime = Table.AddColumn(Source, "ConvertedDateTime", each #datetime(1970, 1, 1, 0, 0, 0) + #duration(0, 0, 0, [UnixTimestamp]), type datetime)
in
AddedDateTime
Generate a date table in Power Query M
If your timestamps are in milliseconds instead of seconds, divide [UnixTimestamp] by 1000 first.
Browse all 145 snippets in the Power Query M Code Snippets, or search the library for something similar to Convert Unix Timestamp to DateTime.