Trump has spent the last three-and-a-half years trashing the US's international reputation as a reliable partner with the rest of the world, and this is just one more example.
While obviously everyone other than the autocrats who dominate and manipulate Trump so effectively hopes that Biden will win in November, and that he will be succeeded in office by another Democrat, it's going to take everyone a very long time indeed to forget that the US once elected someone like Trump and that, after he was elected, he proved that the US's word is worth worth very little because no one in a position of power who might have been able to prove it was, and that international agreements matter to the US, even tried to stop him, or if they did, it wasn't enough.
So yes, everyone would be delighted to have the US back in the WHO, and the Paris Accords, and nuclear test-ban treaties and so on, and taking a leading role in the G7 once again, and NATO, but everyone will wonder, and not without cause, how long it'll last this time, and what's to stop the US from relapsing some years down the line and electing President Tucker Carlson or Tom Cotton or someone similar, and who in the US will even try to restrain them if that happens.