What types of information are you looking for? Oracle used Data Pump for upgrading all of the time. You can also use Data Pump to downgrade. This is just a bit wide open to try and figure out what you are looking for.
isn't there any compatibility issue when the data was exported from 12c and will be imported in 19c?
No, there is no compability issue when going from a lower version to a higher version. You can always do that. It is fully supported and as Dean is suggesting it is used a lot all over. Going the other to a lower version might be an issue if you are using functionality that doesn't exist in a lower version, e.g. a new data type (e.g. native JSON type coming in 20c).
In that case you can use the "version" parameter to make an export compatible with a lower version.
Take a look here:
When going to a newer version there is no need, actually, to specify the version parameter - unless you also specify FULL=Y.
The only time you need to specify version when going to a newer version is from 184.108.40.206 to 12. There was special code added in 220.127.116.11 to help support multi-tenant so when you exported from 18.104.22.168 and imported into 12, extra stuff would be brought forward. Exporting a version 22.214.171.124 with version=12 is not allowed to be imported back into 126.96.36.199. That is the only case that I can think of when you need to specify a 'future' release with any export command.