Having followed the advice provided by QuickPost - and removed the unwanted Shared Calendar from your iPad - you would be best advised to make some configuration changes to your iPad to improve protection from threats such as you have already experienced.
Due to the system architecture of iOS/iPadOS, unless jailbroken (don’t go there!), 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. A further benefit on metered services, such as cellular connections where you data may be capped or chargeable, this not only improves speed but also saves you money.
When using a reputable content blocker product, a high proportion of otherwise inescapable risk encountered when using your Safari browser, or linking to external sources from email, is effectively mitigated before it even reaches you.
A further measure to improve protection is to use a trusted Recursive DNS Service in preference to automatic settings. This can either be set on a per-device basis in Settings, or can be set-up on your home Router. I strongly recommend using one of the following services - for which IPv4 and IPv6 server addresses are listed:
Quad9 (recommended)
9.9.9.9
149.112.112.112
2620:fe::fe
2620:fe::9
OpenDNS
208.67.222.222
208.67.220.220
2620:0:ccc::2
2620:0:ccd::2
Cloudflare+APNIC
1.1.1.1
1.0.0.1
2606:4700:4700::1111
2606:4700:4700::1001
Use of the above DNS services will help to shield you from “known bad” websites and URLs - and when used alongside 1Blocker, provides defense in depth.
I hope this information proves to be helpful in avoiding many online risk that you may encounter when accessing internet resources from your iPad.