I thought one has to stand when the oleh to the Torah says ‘baruchu’ and the tzibbur answer ‘Baruch hashem umevorach’ (Mb 146:4). However most people seem to sit and just do a quick half stand and then continue sitting. Is it correct to say that such a practice is incorrect?
The Rema 146-4 and M:B 146-18 write that the Ashkenazi minhag is to stand while the words Borchu and “Boruch H-shem ..” are said in addition to the actual reading of the torah. . See Kaf Hachayim 146-20 who explains the reason many why people do not stand is based on R’ C. Vital, that the Arizal didn’t stand.
Also see Piskei Teshuvos 146-6.