You're asking if an average person might be able to tell the difference between 900 CE and 1200 CE? Yeah, there’d be some pretty noticeable differences. Despite popular conception, the Middle Ages were anything but static.

Let's say you take your communion in your scenario in the church in your local market town. Suddenly, FLASH! Pow! You’re standing in the same place, but three centuries in the future. We’ll skip the obvious differences—such as the priest and everyone else around you suddenly being completely different people—and take a look around.

You notice the church is different. If it’s the same church, it has aged. Stonework has discolored and artwork has been added or redone.

Or, perhaps it is a completely different church. Taller, with immense, soaring painted glass windows and intricate, graceful pointed arches. Light and airy Gothic architecture, instead of the comparatively more squat and heavy Romanesque architecture of your previous time.

Venturing outside, your town has a castle now. That’s new. A towered edifice of solid stone. You’ve never seen a fortress of stone before. Sure beats the simple wooden tower and palisade that used to be there. The buildings in the town are different, too. They’re still the same basic construction of timber, wattle-and-daub, and the occasional stone, but the style is a little different. And there are more of them.

The people are different, of course. They sound different. It’s your language, but it’s “drifted”. New idioms, new pronunciations and grammar. We’ll assume you can understand it, but it sounds like everyone is speaking “wrong”, or at least with a weird accent.

They’re dressed differently, too. It’s the same basic patterns--Dresses, tunics, leggings, cloaks, and hoods of wool with linen shifts and shirts—but the styles are different. Hemlines, necklines, and patterns are different. The fashionable shape and decoration of hoods, hats, shoes, and cloaks has changed. The style of jewelry; hairstyles, and facial hair is different. The nobles are dressed even fancier than you remember, maybe even outlandish in your opinion.

The armor the nobles are wearing is different. It’s still (chain)mail, but now the mail armor consists of more than just the shirt and maybe a hood. More of the body is now covered in mail. A fully-kitted warrior now is encased in armor head-to-toe. Many of them also have taken to wearing a fabric surcoat over top of their mail. Their shields are different now, too, with a more triangular shape and frequently strapped to the forearm instead of held in the hand. Their shields are painted with rather particular designs now, too. When you ask you’re told it’s something called “heraldry” and that individual nobles have certain patterns that denote them personally. The fashion of their helmets is different; with some the cavalry wear completely covering their face. Their swords are longer, too.

Speaking of the cavalry, it seems the ranks of horse-borne warriors starting to become more common in your old time have become more entrenched. They’re calling them “knights” now. They now seem to constitute a landed noble class.

Returning to the people, there’s more of them. Populations have increased, both in the towns and in the countryside. Europe is starting to experience a population boom. More land is under the plow. The landscape is dotted with more villages, more manors, more of these new castles. The hills outside of town have windmills now, too. You’ve never seen one of those before. Windmills as we think of them first appeared sometime around the 8th or 9th century off in the Middle East and Asia (think Iran, Pakistan, that area), and spread through the Muslim world, which introduced it to Europe. They didn’t become widespread in Europe until around the mid-12th century or so. You might notice water mills are more common now, too.

Venturing out to the countryside, farming technology has improved. Plows are better now. The style of heavy plow just starting to replace the scratch plows in your old time are now commonplace. Padded horse collars, also a new invention in your old time, are also more common, allowing farmers to use more efficient horses as opposed to slower oxen (though oxen are still very frequently used well). Yields are up. In your old time, grain yields were approximately 2:1, meaning for every measure of grain planted, you’d expect to harvest two measures. Now, it’s closer to 3:1, maybe even 4:1.

Continuing to explore, you find more and more that’s different. Art styles have changed. The music and popular songs are different. Narrative epic poems are all the rage, with the Song of Roland being a favorite, and King Arthur stories are particularly popular in France.. Troubadours and “courtly love” and “chivalry” are things now. Tournaments are now a thing. The political landscape is completely different. Slavery is less common. Ships are better now, and now have sternpost rudders. The first, second, and third crusades have come and went. Warrior-monk crusading orders like the Templars and Hospitallers are a thing now. Medicine and surgery, such as it is, has improved thanks in no small part to contact with the Muslim world. In southern Europe, people are starting to play a variant of the Sasanian Persian game “Shatranj” which will become known as chess.

In short, yes, you would be able to tell things were different. The broad strokes may be similar, but the fabric is different.