SQL Server 2019

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DECLARE @xml xml =N'<root>
  <level1>
    <level2>
      <level3 />
      <level3 />
    </level2>
  </level1>
  <level1>
    <level2>
      <level3>
        <level4>
          <level5>
            <level6 here="now is the time for XYZ">
              <options>
                <option this="that" />
                <option me="you" />
              </options>
            </level6>
          </level5>
        </level4>
      </level3>
    </level2>
  </level1>
  <level1>
    <level2>
      <level3>
        <level4>
          <level5>
            <level6 here="this one is not of interest">
              <options>
                <option this="that" />
                <option me="you" />
              </options>
            </level6>
          </level5>
        </level4>
      </level3>
    </level2>
  </level1>
  <level1>
    <level2>
      <level3>
        <level4>
          <level5>
            <level6 here="now is the time for ABC">
              <options>
                <option this="that" />
                <option me="you" />
                <option here="now" />
              </options>
            </level6>
          </level5>
        </level4>
      </level3>
    </level2>
  </level1>
</root>
';

DECLARE @i int = 20; --max nodes

WHILE @xml.exist('
  /root/level1/level2/level3/level4/level5/level6
     [substring(@here, 1, 15) = "now is the time"]
     /options [not(option[@here = "now"])]
   ') = 1
BEGIN

SET @xml.modify('
      insert <option here="now" /> as last into
      ( /root/level1/level2/level3/level4/level5/level6
         [substring(@here, 1, 15) = "now is the time"]
         /options [not(option[@here = "now"])]
       )[1]');
     
    SET @i -= 1;
    IF @i = 0
        BREAK;
END;

SELECT @xml;

(No column name)
<root><level1><level2><level3 /><level3 /></level2></level1><level1><level2><level3><level4><level5><level6 here="now is the time for XYZ"><options><option this="that" /><option me="you" /><option here="now" /></options></level6></level5></level4></level3></level2></level1><level1><level2><level3><level4><level5><level6 here="this one is not of interest"><options><option this="that" /><option me="you" /></options></level6></level5></level4></level3></level2></level1><level1><level2><level3><level4><level5><level6 here="now is the time for ABC"><options><option this="that" /><option me="you" /><option here="now" /></options></level6></level5></level4></level3></level2></level1></root>

(No column name)