Canalway Cavalcade May 6th-8th - Little Venice (a canal junction next to Paddington Station). An annual three-day display of canal boats etc. to raise money for the Inland Waterways Association, the charity that takes care of the UK's canals. Usually has lots of photogenic stuff, see my previous posts about it.
https://waterways.or...-cavalcade-2024
King's official Birthday 15th June - all the usual events e.g. Trooping the Colours, a fly-past, etc. The flypast is usually at 1 PM BST and best seen from the vicinity of Buckingham Palace or on the river east of the Palace - I've had good views from Waterloo Bridge. You need to be near the palace to see the other ceremonies etc., I'm not a fan of crowds so I prefer to go plane-watching, the bridge and river banks aren't usually too badly crowded. If you want to sit to watch the parades etc. you can book a seat, costs £5-£15 depending on location etc.