Do I understand correct by searching and reading here that there is no free seat selection beforehand on TAP flights intra-EU with my basic discount economy ticket? SK Diamond member here, that is.

Only by paying I can choose my seat?

And then at OLCI I am auto-allocated a seat which I may change but I am charged again but I can skip that by exiting without paying and doing OLCI again at T-3 for printing out BP?

If yes on all, I really regret that I bought that ticket