ok... hum i found the reason why i get this error .
This is simply silly: I have 5 devices to tests my apps.
The ones in android 9 and 10 i manually changed their time and date , some days ago to test an app, and i didn't change their date back.
I completely forgot that.
As i renew my cert yesterday these devices were still in "the past" and though, the certificate was not valid cause it was issued in the future for them.
So, no need to worry about Let's encrypt certificates. i simply just racked my brains out on my own.
Thank for the help
@Biswajit and
@oparra btw.
I mark it as solved.