Unsolicited calendar invitations

After you have removed the malicious calendar from your iPad, to prevent recurrence of this or other browser-based attack, you would be well advised to install a reputable Content Blocker on your iPad.

Due to the system architecture of iOS/iPadOS, unless jailbroken, your iPad is not susceptible to traditional malware infection per-se. However, as with all computer systems, there are still vulnerabilities and exploits to which you remain vulnerable.

Browser-based attacks can largely be mitigated by installing a good, trusted, Content and Ad-blocking product. One of the very best and most respected within the Apple App Store - designed for iPad, iPhone and Mac - is 1Blocker for Safari.

https://apps.apple.com/gb/app/1blocker-for-safari/id1365531024

1Blocker is highly configurable - and crucially does not rely upon an external proxy-service of dubious provenance. All processing takes place on your device - and contrary to expectations, Safari will run faster and more efficiently.  Unwanted content is not simply filtered after download (a technique used by basic/inferior products), but instead undesirable embedded content blocked form download.

See the reply from Alex F at: Calendar spam - Apple Community

DJMORESA wrote:

So now how do I remove it

You follow the advice from the link in my initial post.