import re
regex = r"]:\s+([^]]*)$"
s = ("(2021-06-29T10:53:42.647Z) [Denis]: hi\n"
"(2021-06-29T10:54:53.693Z) [Nicholas]: TA FOR SHOWING\n"
"(2021-06-29T11:58:29.053Z) [Nicholas]: how are you bane \n"
"(2021-06-29T11:58:29.053Z) [Nicholas]: \n"
"(2021-06-29T11:58:29.053Z) [Nicholas]: #END_REMOTE#\n"
"(2021-06-30T08:07:42.029Z) [Denis]: VAL 01JUL2021\n"
"(2021-06-30T08:07:42.029Z) [Denis]: ##ENDED AT 08:07 GMT##")
print(re.findall(regex, s, re.MULTILINE))
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