Recurring iCloud Calendar events overspanning and duplicating in 2026

I am trying to organise 2026. This involves recurring events over 5 days repeated every 4 weeks to the end of Jun 26. I am finding it is overspanning by several days as well as duplicating itself over the period by up to 5 times. Anyone else had this problem. Incidentally I am having a similar problem with Outlook on my PC. MS are aware of this & recommending users to try iCloud.com or Yahoo.com

[Re-Titled by Moderator]

Original Title: iCloud calendar recurring events