Going by the telemetry of the seconds before the landing burn and noting the speed vs time, it seems drag was around 40 m/s^2 when it was going at around 3000 km/h. Since drag depends on velocity squared though, it had reduced to just above 10 m/s^2 just before the engines lit at 1250 km/h, and so would quickly become negligible once the engines lit.
Going by Wikipedia, the Super Heavy[1] has 3400000 kg of fuel at launch, so 3% of that is about 102000 kg. For the landing burn, it used 13 Raptor v3 engines[2] to scrub speed. Each Raptor flows about 650 kg/s max, so 3% fuel is enough for about 12 seconds for the 13 engines.
The empty mass of the Super Heavy is about 275000 kg, so about 377000 kg before the landing burn with 3% fuel.
Using the sea-level vs vacuum performance of the Raptor v2 engines, one can estimate that each Raptor v3 produces about 2.45 NM of force at sea-level. So 13 of them would produce about 31.85 MN of force.
Using Newton's second law, F=ma, this gives an initial deceleration of about 84 m/s^2 and about 104 m/s^2 when empty. If we do a rough spreadsheet integration, we get that a burn of roughly 4 seconds is needed to scrub the speed assuming no other forces.
Now, comparing this with reality, the full 13 engines were lit for a little over 5 seconds.
In my simplified calculations I was assuming full throttle the whole way, which obviously isn't realistic, and I also assumed 3% fuel. So over all I think that's a pretty decent estimation.
[1]: https://en.wikipedia.org/wiki/SpaceX_Super_Heavy#Engines