Should I learn Bootstrap?

I do not recommend learning Bootstrap: Years ago when neither flex nor grid layout were available it was a workaround useful for creating responsive layouts. Now times have changed and the latter are available; therefore there is no need for bootstrap, it's just an obsolete layer. You can code any layout you require by use of flex and grid layout. Learn and use these and you will be happy.

A Complete Guide to Flexbox

A Complete Guide to Grid