Welcome!
What macOS version is installed, from "About this Mac..." ?
That model is hardware-constrained to running no higher macOS than version 14.x "Ventura." Ventura fell off the "three most recent versions supported" list a week ago (Sept 15), meaning some apps will not install.
Ex.: MS Office/365 only supports the three latest macOS versions.
Thus our knowing which OS you have can help us give more targeted recommendations, especially for finding alternatives to those that invoke the "last three" limitation.
This is the proper link to iMovie for macOS. It says it still supports macOS 14:
https://apps.apple.com/us/app/imovie/id408981434?mt=12
The other link goes to the iPad/iPhone version.
Also be aware that a 256GB internal drive is practically Lilliputian by today's standards, and cannot be upgraded after the computer goes on the assembly line. Movies can be big files, so you will need to be very careful to not overfill the SSD. You have the option of booting from a larger external drive if you get a fast one (Thunderbolt, not USB).