On 21.7.2021 this ZDNET article wrote about serious vulnerability CVE-2021-3390: https://www.zdnet.com/article/patch-now-linux-file-system-security-hole-dubbed-sequoia-can-take-over-systems/?ftag=TRE-03-10aaa6b&bhid=%7B%24external_id%7D&mid=%7B%24MESSAGE_ID%7D&cid=%7B%24contact_id%7D&eh=%7B%24CF_emailHash%7D
On 22.7.2021 there was kernel update of Ubuntu 20.04 LTS from 5.8.0-59-generic to 5.8.0-63-generic. Was this vulnerability CVE-2021-33909 patched by this update?
The Ubuntu CVE tracker linked to you by @kenn in the comments is going to answer this question instantly.
As you can see, the version of the package 5.8.0-63.71 (in Ubuntu 20.10) will contain the package updates. You can verify your package version by looking at the output of
apt-cache policy linux-image-generic
and looking at the "Installed" lines. If the "Installed" line is equal to or greater than the version strings below (replace the '-' with a dot for the equivalent version matching syntax for APT packaging versions to kernel versions), you are patched.