You should follow the advice and "wipe config during upgrade".
So, unselect the "Keep settings"...
The backup will brick you if you restore it to the new firmware.
The old network config (/etc/config/network) is not compatible with the new DSA switch config.
Usually all other config files are compatible.
("system" may have a wrong LED config, but does not brick you.)
You might also read this for a quick & dirty approach...
The main difference is in /etc/config/network. In general only migrate settings that you have changed, since the default sections of most of the configs have also changed over the years.
What triggers the warning as my target is converted DSA but I still get the DSA warning on every upgrade.
Below is my network config I'm guessing something is triggeing the DSA warning ?
config interface 'loopback'
option proto 'static'
option ipaddr '127.0.0.1'
option netmask '255.0.0.0'
option device 'lo'
config globals 'globals'
option ula_prefix 'fdf6:0e5c:4f41::/48'
config interface 'Adults_Lan'
option proto 'static'
option ipaddr '192.168.1.1'
option netmask '255.255.255.0'
option ip6assign '60'
option device 'br-Adults_Lan'
config interface 'Kids_Lan'
option proto 'static'
option type 'bridge'
option ipaddr '192.168.2.1'
option netmask '255.255.255.0'
config interface 'Wan'
option proto 'dhcp'
option peerdns '0'
list dns '127.0.0.1'
option device 'wan'
option metric '1'
config interface 'Wan6'
option proto 'dhcpv6'
option reqaddress 'none'
option reqprefix 'auto'
option device 'wan'
option metric '2'
option auto '0'
config device
option name 'br-Adults_Lan'
option type 'bridge'
list ports 'lan'
config device
option name 'br-Kids_Lan'
config interface 'Wwan'
option proto 'qmi'
option device '/dev/cdc-wdm0'
option auth 'none'
option metric '3'
option pdptype 'ipv4'
option auto '0'