High percentage of emails going into spam (or getting rejected/not delivered)

Your software
My Mautic version is:4.4.4
My PHP version is: 7.4

Your problem
My problem is:
After Mautic 4.4.4 Upgrade :
A significant drop from consistently 30% and over, to only 5 - 10% in READ mails stats .
Emails are receiving in spam or not delivered.

Could you please help me with this ?

Please check with mail-tester.com for any issues.