Supergirl struggled greatly to lift Fort Rozz, which was said to weigh 1 million tons. This really shouldn't have been a problem, considering that she nearly effortlessly lifted "a million tons of condensed dwarf star matter" at the Fortress of Solitude in a previous episode.
In episode "Solitude" Kara effortlessly lifts the key to the Fortress of Solitude, despite it weighing "a million tons of condensed white dwarf star material" according to James Olsen, however it appears to take Kara a great deal of effort in "Better Angels" to lift Fort Rozz, which weighs "one million tons" according to General Lane.
If the Myriad signal was strong enough and had enough of a range to envelop the planet then sending it above the atmosphere would not stop it from killing a significant portion of the population.
Alex Danvers says to Supergirl before she flies Fort Roz into space that there will be no gravity. In fact, all matter has gravity and it is all over the universe.
Just as with the end of the previous episode, at the start of this one Alex is seen jumping nearly three times her own height in the air (and in full armor at that!). But Alex is a 'normal' human, completely without any super powers, so there's no logical reason how she'd be able to do that. Mind control alone will not somehow magically give a person inhuman strength, let alone practically take 'flight' off the ground like that.
However, the armour could be some kind of Powered Armour that augments the users strength (possibly explaining the reason for what appears to be some kind of cog and hydraulic ram on the arms.)
When Kara is corresponding with Clark via text on a computer, his responses appear instantly after she sends hers, exposing the pre-prepared text that her own return keystrokes are most likely prompting (as opposed to actually coming from another person after reading hers, deciding on an answer and then typing/sending back).
The Redvines lettering on the package Winn is holding is shown in reverse.
Alex flies into space to save Supergirl, and is somehow completely unaffected by the still-active Myriad inside Fort Rozz. There is no plausible reason that Alex Danvers should still be alive.