DriveThruROG has a sale going on. Without adventures a new RPG has little appeal, except for maybe an OSR fantasy RPG since you can generally use those with D&D modules. Going through the first 25 pages I found these items that I'll probably buy, all for AD&D 1E or 2E.

T1-4 Temple of Elemental Evil (1e) - $6, 40% off.

L1 The Secret of Bone Hill (1e) - $3, 40% off. I have this back when WotC was providing some old adventures for free. It's like an RTF file doe the main text and folders with GIFs for each art piece, map, and cover. Sure the content is there but not a nice format so I'd still buy the PDF version.

L2 The Assassin's Knot (1e) - $3, 40% off.

L3 Deep Dwarven Delve (1e) - $3, 40% off. L1 to L3 comprise a connected series of adventures.

Return to the Keep on the Borderlands (2e) - $4.20, 40% off. This is more of a redo of B2 for new beginning PCs rather than a sequel where old and now veteran PCs come back and to find new and tougher monsters. Because I thought this was a sequel I never thought about using it. Now that I know it's a redo I regret, a little, not using this for the change of pace compared to stock B2.

N5 Under Illefarn (1e) - $3, 40% off. N1 to N4 are available as a bundle.