Forgive my ignorance, but why does that look so slow?
It looks like he's having a casual drive around the track.
That's the thing about the best drivers, they can make going fast look so undramatic.
That said, there's a few things at play there.
The lap is midway through a race, rather than a qualifying lap. As such, it's less on edge and more about trying to finish the race. This lap was probably around a 1:18, which is only 2s off Senna's fastest lap of the race, which he won by 9 seconds.
Part of the reason you are perceiving it as slow is actually audio. It sounds like he is short shifting quite a lot in the early part of the lap, very different from the screaming you'd expect from the engine. He could be fuel saving a bit here too.
Add to this that it is upscaled video footage. This never really does well, as the 60fps is mostly machine learning rather than actual found footage. Tom Scott actually has a really good video on this subject.
When it's all a bit smoothed out compared to the 25fps it probably was to begin with, your brain will be used to the images being slightly choppier, and thus movement is sharper and more pronounced in the footage you are used to seeing from the time, so th ebrain thinks its a bit slower. This is one of the issues some people have with modern F1 cameras, is that they are too stable and have a poorly optimised FOV to give a real sense of speed. That said, in return we have really high quality onboards that don't break up and are fantastic for replays and analysis, so it's a compromise.