The forum software can sometimes automatically flag certain posts as suspected spam, depending on certain keywords or links. For example, one of the common keywords is "dating", which can often be used in a way that isn't suspicious, but the software will still flag it. Sometimes you just have to keep editing the post until it's accepted.
I know that some manufacturers (typically Chinese) don't allow for Safe Mode for some inexplicable reason -- but the fact that it works on your brother's Infinix phone makes this unlikely.
I'm afraid I don't know about the ADB stuff, sorry. I'm still suspecting a glitch or fault in the memory chips, so I don't think there's much you can do, since the warranty has expired.