With the way your house is designed you’ll probably have to take him through the childproof gate and down 2 stairs every time he needs to go to the toilet, which sounds a bit like an obstacle course. You may want to toilet time to prevent accidents

Wow, major mission to get to your loo! There are steps you can buy with a smaller seat for toddlers built in are great. But not sure how your toddler will get through the secure gate and down the steps

We used one of those little toilet seats that go over the normal toilet seat. Big kid on the throne!

Is there a room you can put a port-a-loo in which you can flush a similar to what you do a toilet. Obviously your home wasn’t designed with small children needing to go to the toilet which is a shame. A lot of little concentrate so hard on what they are doing that they wait too long to go which results in “accidents”. I know one boy who suddenly refused to use the toilet so they had to put him back in nappies and start toilet training again when he started to show interest.

Definitely give him a bit of time to get used to the idea.

I have found that kids give signs that they are ready. My daughter only recently started using the toilet at 3 years and 4 months once she could get herself on and off it.
I also took the potty away and let her know she is big enough for the toilet. She agreed because according to her, her pee is too big for potty now (as in she is afraid it could overflow).
Give him chances to use the toilet as an exciting new thing, but don’t rush it. I found that rushing things in toilet training can cause regressions due to pressure.

Just try and see how he goes.
If he is resistant, try putting a sticker chart on the back of the toiket door, get his favourite book or toys or make s hame out of it.
If its too much trouble, try brungung the potty in until he is comfortable.

Hope this helps!