Is LearnCpp a good place to build a solid C++ foundation?

Yes, it's a reasonable place to start. Go through the lessons at a pace that lets you understand them, and write and run code as you go. Try changing the examples and working through the exercises rather than just reading.

Once you've got some basics down, make small programs of your own. Getting something wrong and figuring out why can teach you things that are easy to miss while reading.

I wouldn't get too hung up on finding the single best resource. A beginner course only needs to get you far enough to start practicing and building things. LearnCpp is good enough for that, so pick a starting point and give it a proper try.

Expect to revisit C++ concepts using more than one resource over time. The language has been around a long while, and older code can use different practices from what you'd choose for new code. Another explanation can also make a topic click when the first one doesn't.

If you prefer a book alongside the lessons, Starting Out with C++ is another option. Check which C++ version an edition covers when choosing one. An older edition can still be useful, but it won't cover features introduced after its publication.