Disabling IPv6 cuts you off from IPv6 part of the Internet.
If this is not clear, let me repeat: IPv6 isn't the culprit, faulty networking hardware is. As Intel noted back in 2017, virtually all 1G and 10G Intel NICs have compatibility problems with IPv6. The only solid solution is to replace all Intel NICs and/or motherboards containing those NICs as soon as possible.
I spent over 10 hours on the phone with Fios tech support trying to fix this problem, and they wanted to blame everything except what their network guys did during the outage. They were willing to swap out my perfectly fine router for another, but not to escalate the problem to anyone senior. The consistent thread on all of the reported problems of wonky Ethernet behavior on this site was that it happened after an extended local internet outage. You know that Verizon senior tech management knew why they had that long outage, if indeed it was to upgrade their infrastructure to support ipV6. Why didn't they tell anyone?
Finally, the suggestion to just go into the router settings and turn off ipV6 also fixed my problem. Why doesn't anyone in Fios customer support know about this? Why won't they escalate issues to the technicians who were the ones who broke likely tens of thousands of user's connections? I find this so irresponsible of Verizon that I'm tempted to vote with my feet and switch back to Optimum who has upgraded their infrastructure, but they were so wretched during the pandemic when everybody was trying to work for home I'm not sure I'm ready to forgive them yet.
How many times do I need to make this clear?
If turning off IPv6 fixes your issue, it points squarely to the NICs on your computer. They are defective and you need to replace them as soon as possible. If NIC is attached to the motherboard, you need to replace the defective motherboard altogether.
Didn't have issues before doesn't mean the issue is not on your side. Verizon ensures everything until their router is good. You need to fix the hardware on your computer.