I hate when almost after every update you need to restart pc :/ it happens almost every week.
It is common for most AV products. A program update requires you to restart the system.
The alternative method is to disable the AV protection completely, apply the update and restart all the AV services. It is something that Microsoft Defender does. Norton gives you the option to choose whether you want to apply a product update now (which will disable the AV when it performs the update similar to MD) or apply it on the next system restart.
To give you an example, last week I was testing MD in a VM. Almost immediately after I double-clicked on a malware to test, I saw that the Windows Security icon turned red and showed service stopped when I opened Windows Security. Initially, I thought that the malware disabled MD but a minute later I realized, MD had actually received a program update and it was applying the update which needed to stop its service. The timing of my malware execution and MD's update was pure luck/bad luck. (MD failed to detect the malware anyway when I tested again later. The malware added C drive into exclusion. Lol. Needed admin privilege though).
But this is just an example of why most AV products don't want to apply a program update without restarting the system. They don't want to keep you unprotected when it updates. This is for the best.