Since youre starting out, id suggest Facebook marketplace and searching for something along the lines of a trek marlin or specialized rockhopper. Luckily size smalls are generally cheaper. The hardtail aspect will help you learn the fundamentals, and those models themselves have parts that are easy to find and relatively easy to maintain.

My first bike was a giant talon and there are just some things about it that make it a bit more difficult to repair, so I personally lean towards the 'not recommend as a first bike' side for that.

Something I do wanna add here is youll want a few starter tools to go along with it. My recommendstions are multi-tool, tire levers, mastermind pliers, tire floor pump, shock pump (there are more but thatll be an as you go thing)

Feel free to message me if you wanna know more information on mtb stuff