I have done something similar to this. I've found codingbat to be a great resource. The exercises there are not complex and are structured in a way that later exercises build on previous ones. There are more exercises there for Java than Python but at worst it may be useful for prompting ideas.
Now, I have set classroom exercises using some of the ones here, not least because it shows them the tests that are run on the code and I would hope- gets them thinking about test cases, boundaries and so on. Even though I had stated in previous years that some exam questions would be sourced from the site, I have been disappointed to see very few actually engage with the exercises.
Last year I used replit for the first time. Rather than use codingbat for code challenges, I was inspired to create my own version of it where I could actually "see" what people in the class were coding, and I could write my own tests to test their code. I have found this to be extremely useful, and each evening I can review their code submissions, offer suggestions, see where they are having problems- syntax, logic, indentation (python), incorrect docstrings and so on.
These are the codingbat-style exercises I wrote and posted. I can also set up tests that they can run and see what cases fail.
Once a learner views a lab, it forks a copy for them and I can see the clock icon. If they submit it, I will see an hourglass icon and how many tests were passed and then I review the file for things that unit test will not catch- tidyness and so on. Once I have reviewed and accept the submission, it appears with a tick mark icon.
Admittedly it is more work than using something that it "there", but I can jump into their repls and join them in coding, or observe them coding, add comments or chat in real time. If we have to do remote work again this will be really useful, but even in class I find it useful as I do a "walk-through" akin to strolling around the room to see where each learner is at. I am pretty impressed by what is available on this platform.
There are lots of videos that show how to use it- here is just one that I found useful.
Overview of using Teams for Edu