Hi @Anonymous
Thank you for posting.
According to your description, you are trying to get calendar event from SharePoint and sending results via email. But currently stuck the start time and hyperlinks. If any misunderstood, please kindly let me know.
I tried the article you provided and succeeded at the first time. The article is amazing and no problem at all.
Here is my flow and details for your reference:

Related expression(Please pay attention to the bolded part):
Date: formatDateTime(item()?['EventDate'],'yyyy-MM-dd')
Save: concat('<a href="https://hanxia.sharepoint.com/sites/Annas/_vti_bin/owssvr.dll?CS=109&Cmd=Display&List=%7B0D15ADF9-3F36-4AD5-8930-6B5FFA416A8E%7D&CacheControl=1&ID=',item()?['ID'],'&Using=event.ics">Add to my calendar</a>')
In the 'save' expression, we should update the link using our SharePoint URL and list ID.

You could refer this link as below:
Creating iCal (.ics) calendar item links with a workflow (Power Automate or SharePoint Designer) | NateChamberlain.com
Input of compose: replace(replace(replace(replace(replace(body('Create_HTML_table'),'<','<'),'>','>'),'&','&'),'<table>','<table border="3" bgcolor="ffffff">'),'"','"')
In original article, they lost one ‘replace’ formula by mistake.
Once completed, here is the result:


Hope the content above may help you.
Thanks
Anna