NetworkManager and IPv4LL (link-local)

Hello,

i am struggling with the following simple case for a while now.

I have a custom embedded Linux board running Debian Buster and using NetworkManager (1.14.6-2+deb10u1) for networking. Now i would like to get a link-local address as fallback whenever DHCP fails on the eth0 device (pretty normal default behavior IMO), but i never get an address in the 169.254.0.0/16 range assigned - the DHCP case works. Can someone please enlighten me what i am missing?

/etc/network/interfaces

# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback

/etc/NetworkManager/NetworkManager.conf

[main]
plugins=ifupdown,keyfile
dhcp=internal

[ifupdown]
managed=false

[logging]
level=TRACE
domains=ALL

I tried to use the internal dhcp implementation (using libsystemd - as seen in the logs below) since i thought this should minimize issues, but the result is the same as with dhclient and dhcpcd installed (currently i have uninstalled both of them).
dhcpcd seems to be never called at all anyway?

Heres the NM log (journalctl -u NetworkManager) - with mostly removed wifi related stuff:
https://pastebin.com/J4Gdvzgy

"nmcli con up eth0" (eth0 is the NM connection profile name)
ends up with
Error: Connection activation failed: IP configuration could not be reserved (no available address, timeout, etc.)

"eth0" connection profile:

[connection]
id=eth0
uuid=1ea4acce-de15-3854-8c25-97f50ef54906
type=ethernet
permissions=
timestamp=1550139131

[ipv4]
dns-search=
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=ignore

over the weekend i had the following insights:

i created the following wired connections profiles:

nmcli connection add type ethernet ifname eth0 con-name eth0-auto
nmcli connection modify eth0-auto connection.autoconnect-priority 100
nmcli connection modify eth0-auto connection.autoconnect-retries 2 # reduce DHCP retries [since NM v1.6]
nmcli connection modify eth0-auto ipv4.dhcp-timeout 3 # reduce timeout time for each DHCP probe [since NM v1.2]

nmcli connection add type ethernet ifname eth0 con-name eth0-ll
nmcli connection modify eth0-ll connection.autoconnect-priority 50 ipv4.method link-local

This way it seems that NM "falls back" to link-local if no address via DHCP could be aquired.

My initial assumption was that link-local should work as fallback on the same connection, instead of specifying another separate fallback connection.
Can someone confirm if this is the way to go with NM?