After extensive testing I see it was nothing to do with the API, python server, database but an issue with my router.

@neilbdavidson said:
API connection suddenly dead slow
Hi, I am new to development and have been using the API for a data visualization comparison app.
I have been running a script to call the API for data and have had no problems for months.
I am running an SQLite database on a raspberry pi and access to the database via DNS is running fine.
My internet is fine, although my IP changed yesterday as I had to restart the router.
And now script running the API calls has gone from a Formula 1 car to like being stalled in traffic.

I'm a little late, but...
You can see your traffic status at this link.
https://status.themoviedb.org/

I wonder if there is any rate limiting on my account or restrictions due to the changes to my IP.

The limit applies to any API key or IP address.

API Request Limits
First we have this information in the instructions for using the TMDb API.
https://developer.themoviedb.org/docs/rate-limiting

And Travis Bell, the Administrator, has already given us this explanation.

For API Requests:

One of our CDN providers enforces some base level rate limiting to help prevent DDOS attacks.
I believe it's a maximum of:
50 requests per second and
20 connections per IP.

See here: https://www.themoviedb.org/talk/62c7c1b258361b005fd2e747?page=1#62c83b78befd91005007a0c7

For Images:

For image.tmdb.org the only thing we limit is the max number of simultaneous connections.
The limit is the same, 20.

See here:
https://www.themoviedb.org/talk/62edd3ca46aed400917de201#62ee88e7176a940086449cdf
https://www.themoviedb.org/talk/62c7c1b258361b005fd2e747?page=1#6301a107097c49007f60374a
https://www.themoviedb.org/talk/62c7c1b258361b005fd2e747

And...
Is there really no API Rate Limiting?

The original rate limiting (40 requests every 10 seconds) has indeed been been disabled since December 2019.
There are some higher overall limits that still exists to help mitigate different attacks and the like.
I believe they sit around the 50 request per second range.

See here:
https://www.themoviedb.org/talk/6442ced4d35dea02fcfb0fab#6442d4a0d35dea0455fb1a07