#Detect Magic will work

As you've quoted, the first sentence of Create Thrall specifically states it is magic(my emphasis):

At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron.

It is clear that this is magic, and should therefore be detected by detect magic.

For the duration, you sense the presence of magic within 30 feet of you.

##But what will it say? Unfortunately, not much RAW, just that there is magic there. It'll be up to the players/DM to determine if anything more is disclosed and what that would be - or provide clues towards that if they don't want to outright disclose it in entirety.

Detect Magic will work

As you've quoted, the first sentence of Create Thrall specifically states it is magic(my emphasis):

At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron.

It is clear that this is magic, and should therefore be detected by detect magic.

For the duration, you sense the presence of magic within 30 feet of you.

But what will it say?

Unfortunately, not much RAW, just that there is magic there. It'll be up to the players/DM to determine if anything more is disclosed and what that would be - or provide clues towards that if they don't want to outright disclose it in entirety.

#Detect Magic will work

As you've quoted, the first sentence of Create Thrall specifically states it is magic(my emphasis):

At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron.

It is clear that this is magic, and should therefore be detected by detect magic.

For the duration, you sense the presence of magic within 30 feet of you.

#Detect Magic will work

As you've quoted, the first sentence of Create Thrall specifically states it is magic(my emphasis):

At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron.

It is clear that this is magic, and should therefore be detected by detect magic.

For the duration, you sense the presence of magic within 30 feet of you.

##But what will it say? Unfortunately, not much RAW, just that there is magic there. It'll be up to the players/DM to determine if anything more is disclosed and what that would be - or provide clues towards that if they don't want to outright disclose it in entirety.