I have a problem with connecting to RB/751 it ask me for username and password ...
if password i think i knew but I must to do with username ...

At windows PC there no problems I'm just enter the password and everything is work.

make a screenshot of the password window in MacOS and post here.

use CMD+Shift+4 to make screenshot

it looks like that

you chose "WPA enterprise" this is wrong. See what else is in that dropdown menu.

It's disabled so i cant chose anything !

it doesn't look disabled, hmm.

ok, post your wireless AP security profile settings also

I've make exactly my screen shot of what i've got

you have incorrectly configured wireless security in RouterOS. This is how your security profile should look:

UNCHECK WPA EAP:

Yes it can probably be solution because all 4 check boxes is checked I will try it and I will post subscribe.

yes it helps

Maybe there are any tricks too boost RB/751 weak wifi side ?

RB751 actually has a very powerful nearly 1W wireless. So you can't call it weak