Youtube can't comment on Linode via VPN
While we cannot definitively determine if Google is specifically blocking the IP of your VPN Linode solely for commenting purposes, typically, if Google were blocking the VPN's IP, you would be unable to access the web page altogether.
It is possible that Google has flagged this IP as a comment section spam bot, as there has been an increased effort to combat comment spamming following a video from Marques Brownlee. However, from our end, we are unable to confirm this with certainty.
While this is more useful in email sending issue circumstances, it would help to see if your VPN's IP is present on any widely adopted blocklists. If so, removal from those blocklists is a great first place to start.
Although this tool does not directly check your VPN's IP against Google's servers, it can verify if your IP is listed on common blocklists:
Furthermore, I wanted to share a helpful YouTube post that addresses this YouTube commenting issue. Although it does not offer a definitive solution, it does highlight that others are experiencing a similar problem.
There is no problem with google youtube, but youtube can't comment.
I can't comment even if I switch to other regions
Youtube blocks networks associated with VPNs for comments. They do the same thing with nordvpn.