Orbi RBR50 + Verizon Fios - G1100 + Pure Bridging Mode?

What it sounds like is the Fios is still acting as a router and assigning IP addresses via DHCP.  I see no reason to be assigning an IP address to the Fios router in the first place.  Once it becomes a "bridge", there is no reason to talk to it at all.  (I also liked the steps in the web site that was pointed to: https://www.dslreports.com/forum/r31057540-Networking-HOW-TO-Bridge-G1100-So-your-Router-becomes-Primary 

If the goal is to set up a Pi-hole, the Fios does not need to be put in bridge mode and the Orbi could stay in Access Point mode.

When the Pi-hole is configured, it needs to have DNS servers defined.  Most people seem to pick one of the "big five":

https://www.techradar.com/news/best-dns-server 

In the Fios, simply replace the DNS servers with the IP address of the Pi-hole.  "Done"

The way residential routers work is they act as DNS relays.  Every device on the network is told "I am your DNS server", so every DNS request goes to the router.  Anything in the DNS cache is answered immediately.  Anything not in the cache get looked up from the DNS servers that the router is pointed at, answered (and put into the cache).

So, everybody sends DNS queries to the Fios, the Fios sends them to Pi-hole, and Pi-hole sends them "somewhere".

This makes it easy to test the Pi-hole.  Before reconfiguring the DNS entries on the Fios server, manually define the DNS server on any device to the Pi-hole.  That one device will know, "Pi-hole is my DNS server" while every other device thinks Fios is.  Once you are happy with how Pi-hole is working, then change the Fios DNS servers.

As far as the other issue (about wired computers), it would help to know exactly how Fios and Orbi are configured.