Does It Matter Where You Go Through Security at CDG?
 

If I arrive at the TGV CDG station, can I go through security in 2C and walk to 2A or do I have to do security in 2A?

Arriving by TGV doesn’t make any difference to airport security, whichever terminal you will use.
So far as I remember there is a single security entrance for 2A/2C and you can freely move between them after security.

Yes, there is just one immigration and security passage on each side -- 2A-C and 2B-D (2E and 2F have their own.)

And how are the lines for security check nowadays? I haven't read any recent new about the airports collapses. How long do the lines take to go through the checks at CDG?

as always, from 5 min to much more...Sorry but there's no answer to give to this question. It depends on day, time, terminal, etc etc
What I can say is that it's not significantly different than before Covid. Just slightly worse because T1 is still under renovation until end of year so all ops are concentrated in T2 (and T3 but this one is anecdotical).

I’ve never had an issue with the security/immigration lines in 2A. 2E is a different story. Very unpredictable.