From https://xdebug.org/docs/all_settings

This setting can only be set in php.ini or files like 99-xdebug.ini that are read when a
PHP process starts (directly, or through php-fpm), but not in .htaccess and .user.ini
files, which are read per-request.

After all these years, I don't know how you deem that remotely acceptable.

I don't care how hard it is (which I can't imagine it to be), if you can't make that available per-directory then xdebug is basically worthless.

You can't (reasonably easily) have two virtual hosts on the same server one for production and another for development, and easily enable xdebug only on the development one, just to cite the number-one example use case.

Now, I'm pretty sure there are workarounds for that in phpfpm: if you can have different versions of php in parallel, I guess you can have multiple instances of the same version too, running on separate processes using separate main .ini files and directories.

But (a) the complexity of that alone sucks; (b) I'm not sure there's a similar workaround for modphp; (c) what about this: being able to enable/disable xdebug (or change mode) without having to restart php-fpm (or Apache!!) every time. Restarting the entire phpfpm or even apache every time I change that setting is not too much of an issue for me but I'm sure it can be a no-go for a lot of people.

In short it's simply ridiculous that you don't see the necessity of having xdebug.mode settable on a PERDIR basis.