If you're still having the FPS problems, try disabling Xbox DVR since you're on Win 10. Hopefully it helps. Link: https://support.steampowered.com/kb_article.php?ref=6239-DZCB-8600
I see that you're on Win 10. Have you tried disabling Xbox DVR? Link: https://support.steampowered.com/kb_article.php?ref=6239-DZCB-8600 See if this helps.