CreamAPI is widely considered the most "stable" tool for unlocking DLC on Steam. It works by "tricking" the Steam API into believing that your account owns the licenses for specific AppIDs (the identification numbers for DLCs).
A modern alternative often used by advanced users. It supports "Hook" and "Proxy" modes, providing flexibility if standard methods fail. borderlands 3 dlc unlocker steam best
Steam often discounts the Borderlands 3 Ultimate Edition by . CreamAPI is widely considered the most "stable" tool