Prior to Thor: Love and Thunder hitting theaters, Valkyrie actress Tessa Thompson said that her character's arc would involve her searching for "a queen" to rule alongside her in New Asgard. This was never addressed in the movie, and it was generally assumed that the subplot was left on the cutting room floor.
Shortly afterwards, rumors did the rounds that Lady Sif (Jamie Alexander) was initially going to embark on a relationship with Valkyrie, and some new storyboards may confirm that this was the original plan.
At the very least, they reveal that Alexander's perennially underutilized warrior was going to have a bigger role and share the screen with Thompson, and insider MTTSH seems fairly certain that romance was indeed in the air before Marvel Studios decided to go in a different direction.
Sif showed up in the Ragnarok sequel when she was discovered by Thor after losing an arm during her face-off with Gorr the God Butcher (Christian Bale), and was later seen training Axl on New Asgard. Her brief role was largely played for laughs (like pretty much every other character), but there's always a chance Alexander will be given an opportunity to return to The MCU down the line.
As for a potential Thor 5, a recent rumor claimed that the movie was in development with Taika Waititi likely set to return as director, but the trades appeared to debunk the report.
Thor: Love and Thunder finds Thor (Chris Hemsworth) on a journey unlike anything he’s ever faced – a quest for inner peace. But his retirement is interrupted by a galactic killer known as Gorr the God Butcher (Christian Bale), who seeks the extinction of the gods. To combat the threat, Thor enlists the help of King Valkyrie (Tessa Thompson), Korg (Taika Waititi) and ex-girlfriend Jane Foster (Natalie Portman), who – to Thor’s surprise – inexplicably wields his magical hammer, Mjolnir, as the Mighty Thor. Together, they embark upon a harrowing cosmic adventure to uncover the mystery of the God Butcher’s vengeance and stop him before it’s too late.