There are already mentions of LocalSend (i use it for smaller stuff), Syncthing (for keeping folders synchronized, i use it to keep Wine prefixes between my Pc and my Steam Deck up to date) and KdeConnect (I use it for Clipboard sharing); I also use Copyparty, which runs on everything that allows python to run (so pretty much everything) and handles everything from single files to folders, up- and download, drag&drop support, serving mediafiles and so on, with lots and lots of features. give it a try!
There are already mentions of LocalSend (i use it for smaller stuff), Syncthing (for keeping folders synchronized, i use it to keep Wine prefixes between my Pc and my Steam Deck up to date) and KdeConnect (I use it for Clipboard sharing); I also use Copyparty, which runs on everything that allows python to run (so pretty much everything) and handles everything from single files to folders, up- and download, drag&drop support, serving mediafiles and so on, with lots and lots of features. give it a try!
syncthing was new to me. i found it pretty intuitive to set up and am now an enjoyer.