FocusNode: Website Blocker от Ayaan Hafeez

FocusNode blocks the sites that derail your focus.

Add domains like youtube.com or reddit.com to your block list from the
settings page, then flip Focus Mode on from the toolbar popup.

While Focus Mode is on, any tab matching a blocked domain — including
subdomains, so blocking youtube.com also blocks m.youtube.com — is
redirected to a blocked page. Turn Focus Mode off from that page and
you're sent right back to where you were, no lost tabs.

Everything is stored locally in the browser. FocusNode does not
transmit, sell, or share any data.