Telus (and their sub brands like Koodo and Public Mobile) loves to block phone updates for some reason. They published an infographic saying that they test the updates and get the manufacturer to make a new build for them with all of the bugs they find, but I find that hard to believe. I've never seen a custom Telus firmware for any of my phones.
By setting a flag on their SIM cards they can make your Android phone ignore updates, which is what they've done with the Essential Phone. To update it I have a nice little hack that you can use by swapping in another SIM card temporarily.
Here is my phone showing no update available while using my Koodo SIM:
Here is my phone downloading an update immediately after sticking in a Roam Mobility SIM: