Whoops, it looks like Borderlands 4 and Tiny Tina's Wonderlands 2 might have been revealed in a developer's LinkedIn profile.
Developer's accidentally revealing unconfirmed sequels on LinkedIn seems to be a tale as old as time these days, as it's happened once again, this time on the profile of one Randel Reiss. According to Reiss' profile, the developer worked at the Gearbox owned Lost Boys Interactive on a contract basis. In the description for the role, Reiss listed out a number of the games that the contract covered, including titles like the fist Tiny Tina's Wonderlands, Elder Scrolls Online, and more. The more being, quite notably, Borderlands 4 and Tiny Tina's Wonderlands 2.
You can see a screenshot of the profile over on Eurogamer, but since then the description has been changed so that both projects are now "Unannounced Sequel [Unreal Engine 4]" in the same spots they previously were. Seems like this might have been a bit of a panicked change, and the change being as it is certainly lends it some credence; just deleting the mentions could imply a mistake. Of course, it's also important to note the game development is a fickle thing, so such hypothetical sequels are just that until they're officially announced.
In terms of the main Borderlands series, the most recent entry we've had is 2019's Borderlands 3, so not all that long ago. Tiny Tina's Wonderlands, a fantasy-themed spin-off of the stylish shooter, was released last year, and was generally well received at the time of release. Our own review gave it a solid 3/5! It sold well on top of that, so a sequel wouldn't be all that surprising, but given it only came out last year we probably shouldn't expect an official reveal for a while. Though given that Borderlands 3 is a few years old, that might be on the horizon sooner.
In September it was reported that Embrace Group, Gearbox Software's parent company, was considering selling off the Borderlands developer, but nothing's moved there as of yet.