Focus is less about force and more about removing exits.

Trying to focus by sheer effort means fighting every available distraction continuously, which is exhausting and unreliable. Removing the exits, closing the apps, leaving the phone elsewhere, working somewhere without options, means there is nothing to resist. The environment does the work that willpower was doing badly.

Before your next work block, spend two minutes closing off the escapes rather than resolving to concentrate. Make distraction genuinely inconvenient. Focus is much easier when it is the path of least resistance.