Hi and welcome.
Burn out seems to be pretty common with diabetes because it is so relentless to manage. I am only 21 months in so it is hard to comprehend how it must feel to do 40 years with it!
Do you have any of the new tech to help you manage your diabetes? I wonder if that might be a way of reinvigorating your motivation. Even though I am a bit of a technophobe I did find getting the LIbre really exciting and it encouraged me to improve my time in range and experiment and almost treat it like a very slow moving video game trying to keep between the "in range" lines.
I know this year has made things particularly difficult, so maybe you just need to be a bit kinder to yourself and accept that in the current circumstances, your management might not be as good as it has been in the past, but that it will pass and you will get back to good management again. We all know that perfection is impossible and logically there will be times when we do better than others, but at least when we are not doing so well, it leaves plenty of room for improvement!
I hope you find the community here on the forum gives you a bit more perspective and helps to motivate you to pick up your diabetes baton again and run with it, along with the rest of us, who are hobbling along at whatever pace we can manage.