This is probably a hard question that requires experience with lots of published adventures (or lots of researching), but the question itself is simple:
Both the Dungeon Master Guide (DMG) and Xanathar's Guide to Everything (XGtE) provide guidelines on how many magic items a party should have by each level.
In XGtE, a party from 1st to 4th level should get 2 Major Items and 9 Minor. The 2 Major Items should be Uncommon and the 9 Minor are divided in 6 Common, 2 Uncommon and 1 Rare.
In Lost Mine of Phandelver, though, if the characters proceed to complete all side quests, they get the following Major Items when they reach 4th level:
One +1 Longsword (Uncommon) from Redbrand Hideout, one +1 Axe (Uncommon) from Dragon's Tower, one Ring of Protection (Rare) from Old Owl Well, one Staff of Defense (no rarity described, but possibly Uncommon or even Rare), for a total of 4 Major Items, one (possibly two) being Rare.
For Minor Items
You get a total of 18 Minor Items, between scrolls and potions. I didn't check the rarity of each one, but most of them should be Common or Uncommon (the highest level spell scroll I can remember is the Fireball, which is still Uncommon). They do get a Potion of Invisibility, which is Very Rare, as well as a Potion of Flying, Very Rare too.
What the spoilers say is: In LMoP, you get considerably more Magic Items than the guideline says, and some of them are from a rarity higher than the maximum for Tier 1. That doesn't even account for the last chapter, where they should be getting 5th level.
Is LMoP an outlier in the sense that it gives too many magic items? Or do most adventures not follow the guidelines, and instead give more magic items than recommended?
As a note, I understand that (at least for organized play), a Tier 1 adventure shouldn't end without rewarding each player with 1 permanent (i.e. major) magic item, IMHO, so the rewards in LMoP actually make more sense for me than the guidelines in XGtE or DMG.
As a note, I'm mostly interested in long-term multi-tier adventures, like CoS, SKT, HodQ+RoT, ToA, etc., but full-tier adventures (e.g. levels 1-4, like LMoP, already mentioned) are also of interest. Adventures which level range is for 1 or 2 levels aren't exactly on point, since the guidances on both DMG and XGtE are for tiers, so it's hard to compare how many items should be given in that specific level.
Best Answer
Tomb of Annihilation and Storm King's Thunder are definite outliers in regards to the guidance from Xanathar's guide (both of these are excellent books, and I'm going to try to avoid giving significant spoilers).
In ToA, if you only consider items found in treasure blocks in the book, the party would have to stumble into every encounter with magic item rewards on their way through the jungles of Chult in order to come even close by the time they reach Omu (by which time they're supposed to be about 5th level). The tomb itself has a higher concentration of magic items, but 9 of them aren't supposed to be able to be removed from the tomb and most of the remainder are cursed (2 can actually kill a character who uses them with high probability).
Storm King's Thunder leans in the other direction. It's not at all uncommon for parties to be "overburdened" with magic items by the time they're done with the book (around level 10), having more magic items which require attunement than they can attune to, and several besides. For example, one quest awards a minor magic item (of their choice off a list) to every member of the party around level 5.