Sure! Here are some offline RPG games that you can play with 8GB of RAM and with relatively large data sizes:
1. The Witcher 3: Wild Hunt - This open-world RPG offers a massive world to explore, engaging storylines, and challenging combat. The game has high-quality graphics and immersive gameplay that will make good use of your system's resources.
2. Divinity: Original Sin 2 - A critically acclaimed RPG with deep storytelling, strategic turn-based combat, and a rich world to explore. The game offers a high level of customization for your characters and choices that impact the game world.
3. Assassin's Creed Odyssey - Set in ancient Greece, this action RPG offers a vast open world to explore, intense combat mechanics, and a compelling story. The game features stunning visuals and a variety of side quests to keep you engaged for hours.
4. Dragon Age: Inquisition - A fantasy RPG with a rich story, complex characters, and strategic combat. The game offers a mix of exploration, character development, and decision-making that will keep you invested in the world of Thedas.
5. Monster Hunter: World - Embark on epic hunts, craft gear, and take down massive creatures in this action RPG. The game offers a variety of weapons and playstyles to suit your preferences, along with a living, breathing ecosystem to explore.
These games should provide you with hours of offline RPG gameplay on your system with 8GB of RAM. Enjoy your gaming experience!