Both stories feature thoughtful and realistic depictions of teenagers dealing with issues of love and identity in general, as well as the complications of falling in love with your best friend specifically.
Kamisama no Ekohiiki explores some deeper, more philosophical topics as well and generally has slightly higher production value, but both shows are incredibly wholesome and gentle, and frankly perfect for a cozy weekend spent cuddled up on the couch.

Both are musical dramas that feature themes of moving on from a painful first love.
Happy Merry Ending deals with slightly heavier themes than Sing My Crush, but both are fairly gentle, low-angst stories centering healthy relationships and solid friendships.

Both shows are produced by the same team and are notable for their excellent overall quality and the queer authenticity they bring to the table. Blueming falls a little more on the mature side than Sing My Crush, but both series are overall very wholesome and sweet.

Both are wildly charming food-centered romances focusing on characters learning to find joy, love, and meaning both in their existing relationships and in the world around them.
OFC falls slightly more on the mature side of the spectrum than Aki wa Haru, but both are very wholesome stories over all.