OK - appears that there are a lot of this type of Q around, so time to link them together with an example:
My log files contain:
[05-Aug-2021 15:59:19 UTC] PHP Warning: include(): Failed opening ‘custom/metadata/sugarchimpactivity_MetaData.php’ for inclusion (include_path=‘/var/www/httpdocs/include/…:.:/usr/share/pear:/usr/share/php’) in /var/www/httpdocs/custom/application/Ext/TableDictionary/tabledictionary.ext.php on line 106
Looking at line 106, I find:
105 //WARNING: The contents of this file are auto-generated
106 include(‘custom/metadata/sugarchimpactivity_MetaData.php’);
107
That module was uninstalled years ago, so lets find the cause of this:
grep -inr sugarchimpactivity_MetaData.php .
./custom/application/Ext/TableDictionary/tabledictionary.ext.php:106:include(‘custom/metadata/sugarchimpactivity_MetaData.php’);
./custom/Extension/application/Ext/TableDictionary/sugarchimpactivity_.php:3:include(‘custom/metadata/sugarchimpactivity_MetaData.php’);
One is the symptom, and the cause is :
./custom/Extension/application/Ext/TableDictionary/sugarchimpactivity_.php:3:include('custom/metadata/sugarchimpactivity_MetaData.php
So as the extension no longer exists, let’s delete that file.
rm ./custom/Extension/application/Ext/TableDictionary/sugarchimpactivity_.php
rm: remove regular file ‘./custom/Extension/application/Ext/TableDictionary/sugarchimpactivity_.php’? y
Now rebuild the relationships:
by going to the Admin Console->Repair->Rebuild relationships.
followed by a 'quick repair and rebuild and we get the problem resolved 
OBVIOUSLY IF YOU’RE NOT SURE WHAT YOU’RE DOING MAKE A BACKUP - IN FACT THAT’S PROBABLY A GOOD IDEA TO DO ANYWAY. Obviously I take no responsibility for anything relating to this post!