Is it normal that hovering for preview of items in main shops doesn't work? (I haven't played in a very long time or played at all, so I'm not sure how this goes.) Also, how can I get a preview of an item in a main shop?

Yes that's normal. Its to make things more fair. Even out the playing field for restocking.

That's a bummer. I just wanted some new clothes and accessories.. Thank you for your answer!

You could copy and paste the item's name into the Shop Search to look at them instead. You could also look at wearables on Subetalodge or inside the wardrobe

if your goal is to get new clothes and accessories, then Vending will be great for that. It doesn't require any effort and you will get most of the low rarity things that are available, and there are tons of those. Some of the items will even be new items and if you Vend them you can sell them fast at a discount and then buy whatever you want without worrying about restock price because s windfall is a windfall. This is rare and not superprofitable, but it will keep you in new clothes and accessories.