Until now, items below 150eur (bought by private citizens) were not a subject to customs, and some time ago not even for VAT if below 22eur. From july 1st, it's becoming painful, in slovenia for example, 3eur per TARIC code + customs fee + vat.
So, for example you go on alixpress, you buy a silicone phone case for 1eur, a screen protector/foil for 1eur, a phone "sock" for 1eur and a stylus for 1 eur (+whatever shipping, often free).
A few years ago, you'd pay 4eur and get the package. Then they implemented IOSS, so aliexpress has to report the 4eur order to EU, and they charge you 22% VAT on that, so you'd pay 4.88eur directly to aliexpress and they'd pay the tax. Ok, a bit more expensive but doable, unless you want to go outside of eu and order the stuff there and just bring it in with you.
And now? Since they're 4 different items, that's 4 TARIC codes, and that's 3eur per each separate item, so that makes 4eur for items themselves, 4x3eur for customs (16eur together with the item price), then you pay VAT on the full price (including customs!), that makes it 19.52eur + whatever the post office decides to charge for "processing" (used to be ~4-5euros, but usually avoided by aliexpress shippers).
So, instead of 4euros, you'll pay 20-25euros for the same thing, the government taking 20 euros of tax on 4euros of items (even less total worth, aliexpress + chinese shipping has to earn their share too).
I mean sure, they want you to buy locally from dropshippers, but it's still cheaper than that, or from amazon, which will probably be the biggest winner here, and it's not even a european company.
I'm not saying it's perfect, it's not how I would have done it if I was a benevolent dictator, but there are good reasons for it.
So, back then, i'd pay 1eur and get the case (a bit later 1eur+vat), or 4eur (+vat) for all the items. I'd have money left over, that I could spend at a local restaurant, where other people would get paid, for cooking and serving me a meal (and farmers before that). (i won't give the "save to buy an apartment" example, because none of the EU states is actually doing anything to make that peossible for normal people, quite the opposite).
And now I either pay a lot more money to the government (and get notting more back from them), pay a lot of money to a reseller/dropshipper, and get the item a week earlier than from aliexpress. There will be no european phone case company to take over that business, the just 'stuff' will be just more expensive, and we, europeans, will be able to afford less.
And yes, I know, aliexpress will adapt, they'll build warehouses in EU, and iphone cases will be shipped from romania or hungary or somewhere, but they'll still be more expensive. And that's just phone cases... if you have an iphone, you'll find them in aliexpress warehouses locally. But what if you want custom electronics only found on aliexpress? Some niche esp32 board? Some salved controller for a retro computer? Can you count on aliexpress storing those things in EU too? Or will your other hobbies become much more expensive too?