"is the asx 300 actively managed ?" - well, the ASX300 is just a...

"is the asx 300 actively managed ?" - well, the ASX300 is just a list of stocks that make up the top 300 stocks on the market according to a specified methodology. So the ASX300 doesn't buy or sell stocks. But an ASX300 index fund will try to hold shares in quantities that represent the makeup of the ASX300 index.

Lots that you might want (or need) to know about the S&P ASX300:
https://en.wikipedia.org/wiki/S%26P/ASX_300

The answer to your specific question is: Yes, if DroneShield is added to or removed from the ASX300 then any index funds that follow the ASX300 will adjust their DroneShield positions.