Serial communication with a lot of boards

Hi all,

I need to put in serial communication one nucleo board (master) with n (2<n<15) other L432KC boards.
I am in a critical real time environment so I cannot put them in serial:


I need a parallel configuration:

|      |--------|slave_1|
|      |
|      |
|      |--------|slave_n| 

So I need to choose the Board for the master: is there a board with this amount of serial communication port?
If there aren’t board like that: what methods software method can I use to do the job?

Some ST boards have 6 serial lines, but I doubt that’s enough for you. Why not connect over the same bus and (Master -> Many slaves over the same UART) and have a protocol on top which specifies the slave you want to talk to?

Also, is serial actually good? Why not use e.g. I2C? Which can talk to many devices on the same bus.