Lego sets aimed at children are still good! They work as standalone toys, and can also be reassembled, modified and combined. Very few toys are like this.

Adults collect them, true, but there are whole lines dedicated to them.

The "Creator" sets in particular I feel harken the most to the company's roots. They usually have a few different builds per set and include all sorts of unique pieces for making your own creations. They also usually have very fun designs.

I recently built the NES and Game Boy sets and thought both of those were really great. The NES is probably not priced for most people (we try to stay under 10¢ a brick), but the level of detail, whimsy, and mechanics are all really well done. There are hidden scenes and Easter eggs built into the system that are revealed as you build rather than highlighted as features on the box. I was genuinely surprised and had a lot of fun sharing that with my family as we realized what was coming together.

The Game Boy was much more affordable. Less whimsical, but brought back memories of taking apart electronics and marveling at what these circuit boards and components could possibly be doing.

Part of the problem is a solid 1/3 or more of Walmart's LEGO aisle is now various flowers - https://www.walmart.com/brand/lego/botanicals/10056123

These aren't being bought by kids and if the entire market becomes nostalgic adults, eventually they all die.

My kids got a Minecraft set and just use the Warden as a toy and build with all the other bricks and a mat to put the poor lego characters in bad situations where they’ve woken the Warden up (he’s a strong enemy in Minecraft)