The PC versions of both Ghost Recon: Advanced Warfighter games have been delisted from Steam. Ghost Recon Advanced Warfighter 2 is still available as a digital download on Amazon.com, but there's no legitimate way to obtain the first game, other than a used CD-Rom.
Ghost Recon Frontline was announced in October 2021 as a free-to-play "live service" game, presumably a successor to the also-free-to-play Phantoms that ran from 2012 to 2016, with its biggest addition being a battle royale mode in the vein of Call of Duty: Warzone. Highly negative fan reception over it looking and playing too much like its inspiration lead to an alpha test being skipped and a closed beta test before the game was unceremoniously cancelled in July 2022.