The isekai genre of anime has a lot of different "tropes" in it that fans are probably long used to by now. Stuff like the main character being overpowered, trying to build a harem, or using knowledge from their original world to get ahead in life in this new world.
And, that's exactly why the shows that divert from these tropes, even a little bit, end up being more memorable as a result. For example, there are actually a fair number of isekai shows where the protagonist may have some "cheat" ability, but they're awful at using the magic or powers of the world they've been transported to.
7 Satou Kazuma: KonoSuba
Kazuma Satou, the hilariously sarcastic MC of one of the all-time greats, KonoSuba: God's Blessing on This Wonderful World, is quite an interesting character. For one, he has an absurdly high number in his luck stat. So high, in fact, that everything basically works out for him, even if the path to getting there is frustrating or tedious.
Second, he chose to be the "Adventurer" Class instead of the more iconic classes of Thief, Knight, or Wizard. Because of his choice, however, Kazuma can use skills from all classes, albeit at a reduced rate and not with the same level of proficiency. So, while Kazuma does use magic from time to time in Konosuba, it's mostly just basic spells to blow some wind or, more commonly, the Theif-Class Spell called Steal.
6 Youji Itami: Gate - Thus The JSDF Fought There
Next up is a character who is by no means weak, but just doesn't have an aptitude for magic. Youji Itami is the protagonist of Gate - Thus the JSDF Fought There. Itami is a soldier through and through, which means that he's an adult peak physical condition and is well-trained in close combat.
Sure, the guy doesn't have much motivation or work ethic, but when he needs to Itami can do quite a lot. That said, for how much magic is seen throughout Gate, Itami (and the JSDF as a whole) has shown little to no interest in learning it themselves. To be fair, magic is very rare in this other world, with most of the mages being gathered in one area.
5 Sora & Shiro: No Game No Life
Sora and Shiro (or "BLANK" when they're together) from No Game No Life are probably the ultimate examples of what most would define as "underpowered" main characters. They're both physically weaker than a normal human and are anti-social shut-ins whose only real skills are related to games and hyper-intelligence. Of course, in the world of Disboard, these traits make them exceedingly overpowered, but they're still just citizens of the weak Immanity race at the end of the day. Still, at least it's better than being reincarnated as a sword or something.
In any case, they have no capacity for magic like the Elves do, no natural physical talents like the Werebeasts have, and no superhuman abilities like the higher echelon of the 16 Races all seem to have. Yet, despite all this, they still end up beating just about everyone they come across.
4 Katarina Claes: My Next Life As A Villainess - All Routes Lead to Doom
The magic system in My Next Life as a Villainess is a pretty commonly used one in anime, but there are some aspects to it that are pretty unique. For one, it's left pretty vague in general as magic mostly just served as a way of adding individuality to the different romance options in the original game, Fortune Lover, that Katarina was transported to like so many other isekai MCs. Two, there are elemental types of magic that are more common for people to have aptitudes in than others, and Katarina's element of Earth is the most common by far.
Not only that, but Katarina just doesn't have much proficiency in her element of choice or magic at all, taking years to create her patented "Earth Bump" technique.
3 Motosu Urano: Ascendance Of A Bookworm
This next example is another unique case, as Myne (previously known as Urano Motosu on Earth), actually has quite a lot of mana to use magic in her isekai world of choice, especially for a commoner. Nobility in this world tends to be more magically inclined after all. Myne's special case is for two reasons, one, Urano didn't originally come from this world so this is likely some "cheat-like" power, but two, she has something called the Devouring.
This "disease" shows up in just about anyone who has too much mana for their body to handle and requires them to constantly release that mana by storing it in magical tools. Now, Myne is actually relatively gifted in blessings and could probably be good at magic if she worked at it, but the girl is way more interested in making books, and the audience loves her for it.
2 Subaru Natsuki: Re - ZERO
Subaru Natsuki is pretty much the poster boy for what a "default" isekai protagonist is like. He has a cheat-like ability to always "Return By Death", a whole host of women constantly around him, and everyone treats him like he's oh-so-special. Of course, anyone who has watched Re: Zero knows that Subaru doesn't exactly have it easy, and he's not overpowered in the magical department either.
Since the kid wasn't originally from this world, when Puck and Emilia started to instruct him in magic he used a bit too much for his mana capacity which hurt his "gate" the internal organ that controls mana. After that, Subaru used magic a few episodes later, then again when fighting Julius, and another couple of times after that, all while his gate was far from being healed. Now, his gate is basically defective, and it stops Subaru from using anything more than basic magic such as Shamak.
1 Shimazu Toyohisa: Drifters
Last up is Shimazu Toyohisa, the out-of-his-mind battle-crazed protagonist of Drifters that even Oda Nobunaga fears. Now, in this new world that Shimazu has been transported to after death, there are all kinds of historic warriors that existed throughout history (both before and after Toyohisa's time). Not only that, but this world also has a variety of different fantasy races, with the most commonly seen one being the elves.
Toyohisa's group, the Drifters, is constantly going into battle against the Ends', many of whom wield magics related to their life or how they died. The best example is Joan of Arc who seems to have fire magic abilities due to her being burned to death at the stake when she was alive. But Shimazu doesn't have any of that, at least not yet, and gets by in battles primarily using his swordsmanship, tactical mind, and clinically insane hunger for battle which makes his fights all the better on rewatch.