No, as you have set your pihole to 192.168.1.100 dchp should not assign some other device 192.168.1.100.
DNS is NOT DHCP.
DHCP has a range of adresses that will be assigned to end clients
Anyway. Look like the setup is pretty ok now.
Looking at the screenshots... draytec router?
Remember correctly you can not set the DNS in lan settings in draytec.
Have to send you back to the DNS of the isp. change that to 192.168.1.100
Like you did.
Pihole will work, but your admin page will only show requests from 192.168.1.1
As the draytec will do the request for the pc's/mobile.
Some sites mention you can set the lan dns settings in "applications" on the left menu of the draytec
But first lets keep it like it is now.
As a test:
add domain piholetest.com to the blacklist of the pi.
On a pc: ping piholetest.com
The reply should be 192.168.1.100