According to the Memory Alpha Article on the United Federation of Planets:
The United Federation of Planets (abbreviated as UFP and commonly referred to as the Federation) was an interstellar union of planetary governments that agreed to exist semi-autonomously under a single central government based on the principles of universal liberty, rights, and equality, and to share their knowledge and resources in peaceful cooperation, scientific development, space exploration, and mutual defense.
New applicants need to be
Even before the investigation, the prospective member had to meet certain requirements. These were as follows:
It had to have an "advanced level of technology." The Federation's baseline definition of this term was the capability for faster-than-light space travel. (TNG: "First Contact"; Star Trek: Insurrection)
Its government should have achieved stable planetary political unity, demonstrating a resolution of social and political differences and a respect of the rights of the individual. Membership was still considered if there was an isolated faction present that did not want membership, but this was a rare case. (TNG: "The Hunted", "Attached")
No form of caste discrimination was to be practiced. (DS9: "Accession")
So, a new member needs to have an advanced level of technology but by far not the level of the UFP. So, what happens when a new member joins? Humanity reached FTL in 2063 but transporters were only discovered in 2124 and the replicators soon after.
So, does a new member in the UFP simply "get" all the technology? TNG starts around 300 years after the first warp flight. Would the two new members Picard investigated (Angosia III, Kesprytt III) simply have gotten the technology of the UFP, also the technology they are decades or even centuries away of discovering or how is this handled?