Professor Hulk gave a long talk on the rules of time travel in Endgame. These were based upon his logical reasoning. It is possible that those limits were enforced by the method of Time Travel used: move to parallel universes and you are not going to have consequences on your own.
However Loki using TVA gateways did manage to move backwards on the single timeline and have a conversation that altered the future.
I suspect that The Hulk only had logical reasoning to define the rules, where as Loki found out by experience.
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