Would it be possible to initiate a Pi-hole update from the web interface?
If so, could this please be added in the future.
Also, where is the v-6.0 tag?
Some thoughts :
You could figure out what the script was that made the "Reboot System" button work in the older Pi-Hole versions and combine that with the "Gravity Update" output webpage somehow if you feel like developing it yourself.
/EDIT : The first option above won't work according to the post below this one so that brings us to just the second option =>
Another option is to simply have something like https://webmin.com/ running on your Pi-Hole and use the webbased Terminal provided by it to update your OS and Pi-Hole if you want to keep everything within your webbrowser and for whatever reason don't have a local SSH Client available or simply do not want to use one 
No.
The update requires elevated permissions (you need sudo), but the since Pi-hole v6.0 the web interface runs under the pihole user.
This user was designed to have less permissions. This decision was made to increase the system security.
As a result, the web interface can't execute an update.
@rdwebdesign thanks. I Understand.
So, where is the v-6.0 tag?
What do you mean exactly?
Pi-hole has 3 components, each one with its own version numbers.
The current versions are:
Core: Release v6.4.2 · pi-hole/pi-hole · GitHub
FTL: Release v6.6.1 · pi-hole/FTL · GitHub
Web: Release v6.5 · pi-hole/web · GitHub
All of them are v6.x.
You will get these 3 current versions if you install (or update) Pi-hole.
Why do you want the older v6.0?
The optional tags one can use when creating a topic, or reference within a post, such a v5-2. There aren't any tags for v6, and I don't believe users can create new ones.
Oh...
You are talking about Discourse tags.
I think this is on purpose.
If users could create tags, there would be many similar tags for the same subject, like:
v6, v6_0, v-6-0, v-60, v_60, ...
Your suggestion (v-6.0) won't work for 2 reasons: Discourse doesn't allow dots in tags and this tag will look like related to the already superseded v6.0.
I just created a v6 tag.
I think this tag will represent everything related to all versions from v6.0 up to any future v6.x.
Perfect. Thanks. v6 Isn't it beautiful?