Make NetworkManager manage a interface

Question

I am trying to create a WiFi hotspot (from the int connection) on a small test file server running a near stock CentOS 7 (the sort of unsupported 32bit AltArch version), but NetworkManager does not seem to want to manage the device:

$ nmcli dev status
DEVICE       TYPE      STATE      CONNECTION    
enp0s2       ethernet  connected  ext
enp3s1       ethernet  connected  int   
lo           loopback  unmanaged  --            
wlp0s2       wifi      unmanaged  --  

I have tried adding managed=true to /etc/NetworkManager/NetworkManager.conf, and /etc/network/interfaces does not exist. I have tried creating various ifcfg files manually using nano, vim, nmtui and other methods (no GUI is currently available) - it does not recognise it automatically.

How can I get NetworkManager to use the wifi device? It works on other computers, and though I could reconfigure the network with something else, there doesn't seem to be any obvious solutions I have found to get it to work (I have found lots of stuff on getting it to NOT manage devices).

EDIT: Network manager does sort of recognise the custom ifcfg profile - it shows in nmtui profile editor (but not in the 'Activate Connection' bit), and when restarting the process it shows:

Oct 21 18:05:53 HOSTNAME network[6076]: Bringing up interface USB-Hotspot:  [  OK  ]

but does not seem to associate with the device despite having the correct MAC and interface addresses.

EDIT2: Here is one of the inital files (/etc/sysconfig/network-scripts/ifcfg-USB-Hotspot - MAC etc blanked)

HWADDR=XX:XX:XX:XX:XX:XX
ESSID="26-3"
MODE=Ap
KEY_MGMT=WPA-PSK
TYPE=Wireless
BOOTPROTO=shared
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
NAME=USB-Hotspot
UUID=36b6cb89-6f59-453a-84d9-1ef7ff35f187
DEVICE=wlp0s2
ONBOOT=yes
WPA_ALLOW_WPA=yes
WPA_ALLOW_WPA2=yes
NM_CONTROLLED=yes
MAC_ADDRESS_RANDOMIZATION=default
ZONE=public

I have just tried various other incantations of it as well, including this (based on the working config file off another computer, using the same wifi adapter):

HWADDR=XX:XX:XX:XX:XX:XX
ESSID="wtop"
MODE=Ap
SSID_HIDDEN=yes
TYPE=Wireless
BOOTPROTO=shared
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=Hotspot
UUID=bb8842f3-79ae-4f9c-ae93-838d064e4fa4
ONBOOT=no
ZONE=public
KEY_MGMT=WPA-PSK
MAC_ADDRESS_RANDOMIZATION=default

I when I first installed this ages ago I also had a problem that the NIC added post install was also not managed, but I reinstalled CentOS for something else and it worked then. I have got this sort of thing to work using NetworkManager and other things (hostapd, udhcpd, etc), but this is a bit odd.

Also, nmtui:

]

And when created manually I did do the required /etc/sysconfig/network-scripts/keys* files.

EDIT3: This works on a laptop, same wireless adapter - weird:

HWADDR=XX:XX:XX:XX:XX:XX
ESSID="testing"
MODE=Ap
KEY_MGMT=WPA-PSK
SSID_HIDDEN=yes
TYPE=Wireless
BOOTPROTO=shared
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=USB-Hotspot
UUID=8b6a2f48-ab82-412d-bf22-36ec2120ff2a
ONBOOT=yes
MAC_ADDRESS_RANDOMIZATION=default
WPA_ALLOW_WPA=yes
WPA_ALLOW_WPA2=yes

Answer 1

After many trials and errors to force Network-Manager to handle unmanaged network devices I had on last resort which -- helas -- did the trick:

touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf

This is also mentioned here, here and with multiple variations also here.

If one had known what to look for in the first place.. so many red herrings..

Edit: was on Ubuntu 18.10, so after all those years, still valid.

HTH