Whether it is better depends on the factors used. Operationally the numbers are easy to do then you just have to figure out the manufacturing emissions. But yes in my case here it is better to buy a new BEV. The numbers are actually pretty easy to do from a carbon emissions point of view especially for the operation.

Here is an example of the math and I am doing it in metric because that's what we use here. I drive around 24,000 kms a year. So if I bought a gas car (or kept using one that I already bought) I would use 1882 liters of gasoline to drive that distance if the car got 7.84 L per 100 km (30 MPG). Each liter of fuel emits 2.3kg of carbon when burned and then there is another 0.4 kg of carbon per liter to extract and refine oil into gas. So a year i am looking at 5081 kgs of CO2 to drive that distance in the used gas car.

My BEV gets around 6.2 kms per kWh in efficiency on average. So to drive 24,000 kms will require 3871 kWh of electricity. Charging losses will add about 10% onto that number so make the number 4100 kWh a year used. Our grid produces about 45 grams of CO2 per kWh produced. So that is 184.5 kgs of CO2 or 28 times less CO2 then the gas car above.

See I think this is where people just don't really understand these numbers. They believe that the gas car and BEV might be far closer in operational emissions then they are. And they possibly could be on a dirtier grid. But on a clean grid the amount of CO2 from the car is almost negligible. In fact my car emits less CO2 in operation then I breath out in a year. And based on this (a negative view of electric cars) a 75 kWh battery will emit about 4500 kgs of CO2 to build the battery.

https://8billiontrees.com/carbon-offsets-credits/carbon-footprint-of-electric-cars-vs-gasoline/

So that is a tiny amount compared to the 15,243 kgs of CO2 the gas car will emit in operation alone over the next 3.

So again it is far better here to buy a new BEV then keep driving a used gas car if you want to reduce your carbon emissions where I live and with my numbers. Where you live and with your numbers it might be different.