To put it mildly, and this is not a criticism - it's impossible to cover so long a period in a short video - the video is simplistic, leaves out
many cogent details, and the maps with arrows plus those with large areas settled by the barbarians can be very confusing. The video has some areas where I disagree, but have to accept that other interpretations are possible.
Specifically, although I agree with the assumption that the Battle of the Frigidus was a major factor, and Stilicho almost certainly withdrew troops from the frontier to defend Italy, there are other factors either attributed without evidence, overlooked or skipped over.
For example, the Romans were never seen as 'invincible', but were acknowledged as extremely dangerous and an attack was likely to provoke a response. At least until later. If seen as invincible, no one would have dared to attack. And there are several defeats throughout the period (upcoming: Hughes, probably late 2022/early 2023, but covering Rome's existence). Also, there is no contemporary evidence that the Rhine was frozen (although this is acknowledged in the video).
However, overlooked is the fact that the numbers of people crossing the Rhine was probably far smaller than previously thought, and although there is the acceptance that the loss at the Frigidus was a major factor, the video covers neither the loss of the Illyrian recruiting grounds to the Eastern half of the Empire, nor Stilicho's plan to use Alaric in an Invasion to recover Illyricum, which would also account for the focus being away from the Rhine.
In my opinion, these are just a few things that should be borne in mind.
(Other opinions are available!!)