Microsoft SharePoint Server Spoofing Vulnerability

According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do?
In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) that contains a specially crafted file that is designed to exploit the vulnerability. However, an attacker would have no way to force the user to visit the website. Instead, an attacker would have to convince the user to click a link, typically by way of an enticement in an email or Instant Messenger message, and then convince the user to open the specially crafted file.

According to the CVSS metric, privileges required is low (PR:L). What does that mean for this vulnerability?
The attacker must be authenticated to the target site as at least a Site Member.

According to the CVSS metric, successful exploitation of this vulnerability could lead to some loss of integrity (I:L)? What does that mean for this vulnerability?
Integrity is impacted as XSS allows an attacker to add their malicious script to fetch victim's sensitive info or to change DOM execution.

I am running SharePoint Server 2019 and there are multiple updates available. Do I need to install all the updates listed in the Security Updates table for these versions?
Yes. Customers should apply all updates offered for the software installed on their systems. If multiple updates apply, they can be installed in any order.

Security updates
16.0.10399.20005 — https://support.microsoft.com/help/5002402
16.0.10399.20005 — https://support.microsoft.com/help/5002403
16.0.16130.20548 — https://support.microsoft.com/help/5002416