I had the exact same problem. I finally found a solution here.
Specifically, that site says:
“If Apache is anything less than version 2.0 OR you host does not use Apache, then you only have one choice for permalinks.: /index.php/ needs to be included as part of the permalink structure.
Example:
https://www.yoursite.com/index.php/this-is-what-i-think. “
Since my “Forbidden” message said Apache/1.3.29 , that’s what I did.
I did the following:
— delete .htaccess
— Go to the permalink tag in the options section of WordPress, then first clicking the radio button for the “date and name based”. This automatically filled in the field next for Custom. Manually edited that field and inserted /index.php/ so that it now reads:
/index.php/%year%/%monthnum%/%day%/%postname%/
Click radio button for Custom.
— Click Update Permalink Structure.
It then still said I should now update the .htaccess, but I just ignored this.
Seems to work. Of course, URLs are more unwieldy with the /index.php/ but nothing else worked for me.
m.
