Mint Wi-Fi hotspot not seen by smartphone

[mohican]

Hello,

I've created* a Wi-Fi hotspot from my computer running Mint 19.2 (xfce).
The Wi-Fi network can be seen and connected to from another computer (running Mint 19.3 (xfce))
But our two smartphones can't see it.

Why ?
I found the band switch (modifying the connection), I chose 2,4 GHz but it did not change.

What could I do ?
Thank you.

(*This is how I did it :
the computer is connected to the Internet with a Ethernet cable.
click on the network indicator
create new Wi-Fi network)

[JeremyB]

I know at one time Mint and Ubuntu used ad hoc mode by default for wifi hotspot and spartphones usually ignore them because of it