Windows 10 sync problem

Damm even I am having a similar kind of issue, I have searched all over the internet and even have posted on number of threads on different forum, no solution seems to work. I am really frustrated, can anyone of you here help me resolve this issue, I am very much tired now.

No offence, but just want to point out that it's most likely your fault. The last update messed up with mail cartification. Avast users got the same exact problem Avast Community right after the last update which has the same patch notes as yours antivirus.

Avast promptly released a hotfix this. Since Avg and Avast share the same code/updates/features, I highly doubt it's actually my PC behaviour. 

On a side note, I was checking the mail ports in geek:area advanced settings of AVG (and found nothing wrong with them), and I just discovered a rather gross bug. When you select "clear scan history", AVG interface completely breaks, I had test this on different PCs to confirm, and had to run a repair on all of them to fix the broken icons.

After the last update (21.5.3185 version), my Mail and Calendar apps (both up-do-date) stopped working properly, since I can no longer sync my accounts. I tried to reinstall them, delete and re-add my gmail accounts, all for nothing. The strange fact is, only gmail accounts got this weird behaviour, my microsoft account (live.com) still works perfectly fine. Then I found the problem:  it seems as though Avg (I suppose mail protection or web protection) is causing this ("Your mail certificate is invalid" error 0x80072F0D displays on screen). Turning avg protection off allow the accounts to sync a they should. The problem appeared after the last update. I'm using windows 10 64 bit 21H1, everythings's updated and OS is original.

Hello Paul. 
Thank you for writing us here.
May I know which AVG product are you using? Are you experiencing the exact same issues reported by Andrea?
We'd request to write your own post containing more details about the issues you are experiencing.

No offence, but just want to point out that it's most likely your fault. The last update messed up with mail cartification. Avast users got the same exact problem Avast Community right after the last update which has the same patch notes as yours antivirus.

Avast promptly released a hotfix this. Since Avg and Avast share the same code/updates/features, I highly doubt it's actually my PC behaviour. 

On a side note, I was checking the mail ports in geek:area advanced settings of AVG (and found nothing wrong with them), and I just discovered a rather gross bug. When you select "clear scan history", AVG interface completely breaks, I had test this on different PCs to confirm, and had to run a repair on all of them to fix the broken icons.

It seems as though I was able to fix the problem. First off, I launched the rapair function. Then I entered in settings-> geek:area-> and deselected-reselected "check for SSL connection" and "ignore local comunication" under the mail shield options. Disabling and re-enabling those solved the issue after a reboot.

Damm even I am having a similar kind of issue, I have searched all over the internet and even have posted on number of threads on different forum, no solution seems to work. I am really frustrated, can anyone of you here help me resolve this issue, I am very much tired now.

Paul, we're more than willing to help you. 
Which AVG apps are installed on your PC? If you are a paid user of AVG, we'd once again request you to write your own post rather than some other's thread. It will help us to locate your AVG account quickly and provide required help.

We certainly understand, Andrea.
However, we'd request you to reinstall the AVG app once and monitor the issues.
If they persists, we'd request you to reconnect with our remote assistance team as suggested in our previous post. They would be glad to collect some diagnostic logs from your PC and escalate this issue to our senior technical team for further analysis. 
Appreciate your patience and efforts so far.