tampermonkey github pull request mark file as Viewed keyboard shortcut. Found it in https://github.com/orgs/community/discussions/10197, but modified it over time because I found some bugs.

alternative.js

// ==UserScript==
// @name         GitHub PR Review Mode Improvements. Credit: https://github.com/orgs/community/discussions/10197#discussioncomment-14710611
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  Automatically advances to next file after marking a file as viewed, outlines the active file, and focuses the "Viewed" checkbox for keyboard navigation
// @author       You
// @match        https://github.com/*
// ==/UserScript==

(function() {
    'use strict';
  const CLASSNAME_ACTIVE = "br-reviewmode-active";
  const STYLE_ACTIVE = `outline: 3px blue solid;`;

  /** @typedef {Object} Selectors
   * @property {string} attribute - Name of attribute that changes when a file is marked as viewed
   * @property {string} button - Selector for the "Not Viewed" button/checkbox within a diff
   * @property {string} diff - Selector for the entire diff container for a single not-yet-reviewed file
   * @property {string} filesChangedContainer - Selector for top-level container around all file diff views
   */

  /** New Github PR Files Changed review page (late 2025 preview)
   * @type {Selectors}
   */
  const SELECTORS_NEW = {
    attribute: "aria-pressed",
    filesChangedContainer: 'div[data-hpc="true"]', // brittle, fix this
    button: 'button[aria-label="Not Viewed"]',
    diff: `div[role=region][class*="Diff-module"]:has(button[aria-label="Not Viewed"])`,
  };

  /** Legacy review PR Files Changed review page (opted out of late 2025 preview)
   * @type {Selectors}
   */
  const SELECTORS_LEGACY = {
    attribute: "data-file-user-viewed",
    filesChangedContainer: 'div[data-target="diff-layout.mainContainer"]',
    button: 'input[type="checkbox"]:not(:checked)',
    diff: `.js-details-container[data-details-container-group="file"]:has(input[type="checkbox"]:not(:checked))`,
  };

  const selectors = document.querySelector(
    SELECTORS_LEGACY.filesChangedContainer
  )
    ? SELECTORS_LEGACY
    : SELECTORS_NEW;

  const filesChangedContainer = document.querySelector(
    selectors.filesChangedContainer
  );
  if (!filesChangedContainer) {
    console.warn("ReviewMode: could not find 'Files changed' container");
    return;
  }

  const style = document.createElement("style");
  style.innerHTML = `.${CLASSNAME_ACTIVE} { ${STYLE_ACTIVE} }`;
  document.body.appendChild(style);

  /** @type {HTMLElement | null} */
  let lastDiff;

  function advanceDiff() {
    lastDiff?.classList.remove(CLASSNAME_ACTIVE);
    /** @type {HTMLElement | null} */
    const nextDiff = document.querySelector(selectors.diff);
    if (!nextDiff) {
      // No more to review
      return;
    }
    nextDiff.scrollIntoView({ block: "center" });
    nextDiff.classList.add(CLASSNAME_ACTIVE);
    /** @type {HTMLElement | null} */
    const nextButton = nextDiff.querySelector(selectors.button);
    nextButton?.focus();
    lastDiff = nextDiff;
  }

  const observer = new MutationObserver((mutations) => {
    mutations.forEach((mutation) => {
      if (
        mutation.type === "attributes" &&
        mutation.attributeName === selectors.attribute
      ) {
        advanceDiff();
      }
    });
  });

  observer.observe(filesChangedContainer, {
    attributes: true,
    subtree: true,
  });

  advanceDiff();
})();

script.js

// ==UserScript==
// @name         GitHub PR review keyboard shortcut
// @version      0.3
// @description  Mark file as "viewed" on GitHub PR UI when hovering and pressing 'Escape' key
// @match        https://github.com/*
// @author       dvdvdmt, nbolton
// @source       https://github.com/orgs/community/discussions/10197
// ==/UserScript==

(function() {
    'use strict';

    if (window.disposeMarkAsViewedByEscape) {
        window.disposeMarkAsViewedByEscape();
    }

    window.disposeMarkAsViewedByEscape = start();

    function start() {
        window.addEventListener('keydown', handleKeyDown);
        return () => window.removeEventListener('keydown', handleKeyDown);
    }

    function isInEditableArea(el) {
        if (!el) return false;
        // If the target or any ancestor is input/textarea/select
        if (el.closest && el.closest('input, textarea, select')) return true;
        // If the target or ancestor has contentEditable=true (or is contentEditable)
        const editable = el.closest && el.closest('[contenteditable]');
        if (editable) {
            const ce = editable.getAttribute('contenteditable');
            // treat empty string or "true" as editable; also fallback to isContentEditable
            if (ce === '' || ce === 'true' || editable.isContentEditable) return true;
        }
        // Some GitHub editors use role="textbox"
        if (el.closest && el.closest('[role="textbox"]')) return true;
        return false;
    }

    function markFileAsViewed() {
        console.debug("Marking file as viewed");

        const fileElement = document.querySelector(`[id^="diff-"]:hover`);
        if (!fileElement){
            console.debug("No file element under cursor");
            return;
        }

        const buttons = [...fileElement.querySelectorAll('button')];
        if (buttons.length === 0) {
            console.debug("No buttons found in file element");
            return;
        }

        // GitHub sometimes localizes the label; we attempt to match the visible label
        const checkbox = buttons.find(btn => btn.textContent && btn.textContent.trim() === 'Viewed');
        if (!checkbox) {
            console.debug("No 'Viewed' checkbox/button in file element");
            return;
        }

        checkbox.click();
    }

    function handleKeyDown(event) {
        // Only act on plain Escape without modifiers
        if (event.key !== 'Escape' || event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) {
            return;
        }

        // If focus is inside any editable input/textarea/contentEditable, do nothing
        if (isInEditableArea(event.target)) {
            return;
        }

        markFileAsViewed();
    }

})();