Case sensitiv ?

Where are you trying to add a link ?

Have you tried turning the link into uppercase via css :
https://www.w3schools.com/cssref/tryit.asp?filename=trycss_text-transform

Cheers,
The RSS Post Importer Nerd

Resolved ?

Not at all !

??

try to add this feed and look what it is done via the plugin

https://poitiers.snes.edu/OLD/spip.php?page=backend&id_rubrique=39

I need a solution, too, to add feed-links with uppercase within. Is there any solution?

Yes, send me an email so I can send you the next release candidate with an improvement for this (along with several other improvements) , if you have a premium RSS Key, if not, please wait a couple of days and the 2.0.18 should be out asap with all those fixes.