Shifters traditionally fit into the Eberron campaign setting, with Eberron: Rising from the Last War and Wayfinder's Guide to Eberron being useful sourcebooks for this setting. There are no specific modules set in Eberron, but a DM may choose to shift a module there. If your DM is running a specific module, chat with them first to see if a Shifter will work in their setting. There's no reason to exclude Shifters from any campaign setting, although some modules, such as Curse of Strahd, which are human-heavy, may not be as compatible.