The Sleuth of Ming Dynasty

Both dramas about the royal court affairs
and detective investigations
Both have Bromance between male leads I think

If you want more bromance dramas in ancient china times, then this is worth checking out.
I love the special relationship between the three different main characters, a powerful eunuch, a low ranked official, and an imperial guard. They are so different but work together so well, worth checking out.

Both have strong chemistry between the two male leads / Bromance

Both are detective based; The sleuth of Ming Dynasty is more investigation and crime solving heavy

Both are adapted from BL novels but without explicit BL

The sleuth of Ming Dynasty is a historical based drama while Guardian is fantasy based