Click on https://reference.wolfram.com/language/ref/Solve.html

Click on the orange Details and Options

Read the items that document the Solve behavior when domain information is included.

I think it actually refers to point 2 that Reals from Solve[{},{}, Reals] (I saw this recently in a youtube video: https://www.youtube.com/watch?v=_155Zu-al3A&t=529s (8:30-8:50 min)):

Only the solutions of the system of equations are restricted to be real, but the variables in the 7 equations are not restricted to be real.

Sorry, I use Wolfram only recently...

Then another question is if I want to set a condition for some variables in equations Eq1,...,Eq7, for example, to restrict L1 and L2 to be positive numbers (L1 >0, L2>0) or real (L1 - Real, L2 - Real), how do I do that?

With corrected syntax:

@Mariusz Ivaniuk

What I want to ask is:

1. Only the variables in the 7 equations are restricted to be real, but the solutions of the system of equations are not restricted to be real (for example, they can be complex values as well, if such values exist)? or
2. Only the solutions of the system of equations are restricted to be real, but the variables in the 7 equations are not restricted to be real? or
3. Both the variables in the 7 equations and the solutions of the system of equations are restricted to be real?

Oh, yes, with numeric values the results are probably easy (as you said) to compute, but beside the numeric results, I want firstly to have the symbolic results. Matlab, Maple, and even Mathcad can solve symbolically this system of equations. Another question here will be: if we restrict the result to be a real one (and that is because Mathematica cannot solve symbolically this system of equations if we do not restrict the results to be real ones), and at some point we want to have/see even the complex results (of course, if they exist) of this system of equations, then what will we do? Or, maybe we can hope that system of equations like above one to have only the results that are real.

Also, do you know the answer for this question: if I want to set a condition for some variables in equations Eq1,...,Eq7, for example, to restrict L1 and L2 to be positive numbers (L1 >0, L2>0), how do I do that?