My recommendation is to first read Scott Meyer's book "Effective Modern C++". This will give you a tour of the language features in modern C++ without wasting your time teaching you the basics, which are going to come back to you rather quickly anyway. It's a short book and it's not going to cover everything you need to know in modern C++, but you can read it quickly and after you've read it and done a little C++ programming you'll know which things you want to dive into further.
As for what kind of programs to write to get excited about C++, I personally feel like systems programming is the area where C++ really shines, and I would encourage you to find some kind of project in this area that excites you. For example, write a simple high-performance key-value database using mmap. Write a httpd using boost::asio or even just using epoll directly. Something like this. There are a million projects to choose from, just pick something that you find interesting.
With regard to CUDA, while it is true that it's an area where people use C++ today it's also fairly different from writing regular C++ programs since you need to use different tooling and the programming paradigm is a little different. If you're really passionate about CUDA I don't see any reason why you couldn't start there, but I think it would be easier to do regular userspace C++ programming first and then transition into CUDA later if you are interested in it.
I definitely empathize with your post since I haven't done any C++ in 10 years and I'd like to get back into it. The last job I had using it wasn't on C++11 yet and it seems like there's been a whirlwind of progress since then.
The place I see small C++ making gains is in IOT. With https://platformio.org it makes it a breeze to get a compiler to target the platform you want.
ESP32 modules have wifi/bluetooth and are $19 for 3 on Amazon and programmable over usb.
https://www.amazon.com/D-FLIFE-ESP-WROOM-32-Bluetooth-Develo...
As far as projects... I probably wouldn't pick C++ for a tiny program.
But if that's what you want to do, maybe check out some of the new coroutine functionality. Some toy async web stuff might be an interesting challenge. There are plenty of services with public REST APIs. Make a toy client in C++.
You could try writing a raytracer, or physics sim, or small tools that would have been difficult/annoying previously (like dealing with JSON). You could revisit writing win32 apps. The WebView2 lib (which is Edge) is self contained-ish and interesting to learn with (lots of async).
For a taste of what is possible with openFramworks, take a peek at this youtube series by Lewis Lepton: https://www.youtube.com/watch?v=dwt2NAd1ZYY&list=PL4neAtv21W...
https://gist.github.com/bkaradzic/2e39896bc7d8c34e042b
I would advise to read the code and tinker with Dear Imgui.
Less time being bogged down in the quagmire of C++ "features".