Getting data from Postgres through Linked server of SQL
I think the problem is datetime2 is not a postgres data type:
convert(datetime2, &quot;2020-01-01 00:00:00.0000000&quot;)

The openquery statement exucute in the target database the query between '' so it must be written in the targewt dialect
try this

select * from openquery(SALESFORCE,'select closeddate from case where
closeddate &gt; cast(''2020-01-01'' as date)')