How to fix the «Invalid input datetime format» / «Failed to parse time string» / «The timezone could not be found in the database» product save backend error in Magento 2.3.2?

Replace the line:

with the following one:

$date .= ' 00:00';

Hey this doesn’t work for me. Can you give any hints as to why it wouldn’t work?

Changed the code as above and re-compiled the code but it doesn’t change anything as it still errors.