stardb-achievements-export.js

javascript:(function () {
  fetch(`https://sg-public-api.hoyolab.com/common/badge/v1/login/info?game_biz=hkrpg_global&lang=en-us&ts=${Date.now()}`, { credentials: 'include' })
    .then(res => res.json())
    .then(body => {
      fetch(`https://sg-public-api.hoyolab.com/event/rpgcultivate/achievement/list?game=hkrpg&game_biz=hkrpg_global&badge_region=${body.data.region}&badge_uid=${body.data.game_uid}&show_hide=false&need_all=true`, { credentials: 'include' })
        .then(res => res.json())
        .then(body => {
          const data = {
            hsr_achievements: body.data.achievement_list
              .filter(a => a.finished)
              .map(a => Number(a.id))
          };
          const json = JSON.stringify(data, null, 2);
          const blob = new Blob([json], { type: 'application/json' });
          const url = URL.createObjectURL(blob);
          const a = document.createElement('a');
          a.href = url;
          a.download = 'stardb-achievements.json';
          a.click();
          a.remove();
          alert(`Exported ${data.hsr_achievements.length} achievement(s).`);
        });
    });
})();

Bookmarklet that can be run on HoYoLAB > Honkai: Star Rail > Toolbox > Upgrade Recommendations.
Or Game Tools shortcut from in-game phone.
https://act.hoyolab.com/sr/event/cultivation-tool/index.html?game_biz=hkrpg_global&hyl_auth_required=true&hyl_hide_status_bar=true&hyl_landscape=true&hyl_presentation_style=fullscreen&mode=fullscreen&utm_campaign=CultivationTool&utm_id=6&utm_medium=tools&utm_source=hoyolab&win_mode=fullscreen&lang=en-us&bbs_theme=dark&bbs_theme_device=1#/tools/suggestion

Preliminary research done by @Modder4869.