An additional note, I attempted to use a fresh download of Piwigo 14.3.0 and experienced different behavior: Using 14.3.0 I was able to access the installation.php page (after setting chmod 777 _data) and filled out the form with the username, database info, etc. After clicking the "Start Installation" button I again encountered a completely blank screen. /var/log/apache2/error.log contained the following new errors:

[Sun Jun 30 10:52:49.788380 2024] [php:error] [pid 440] [client 192.168.0.44:54132] PHP Fatal error:  Give write access (chmod 777) to "_data/" directory at the root of your Piwigo installation in /var/www/html/photos/include/functions_html.inc.php on line 389
[Sun Jun 30 10:55:13.356120 2024] [php:error] [pid 274] [client 192.168.0.44:59566] PHP Fatal error:  Uncaught TypeError: fputs(): Argument #1 ($stream) must be of type resource, bool given in /var/www/html/photos/install.php:334\nStack trace:\n#0 /var/www/html/photos/install.php(334): fputs()\n#1 {main}\n  thrown in /var/www/html/photos/install.php on line 334, referer: http://192.168.0.23/photos/install.php?language=en_US

Thanks for the reply. I have taken the following troubleshooting steps:
Permissions: the entire piwigo installation directory is owned by www-data with 755 permissions, set recursively:

root@mariadb:~# ls -l /var/www/html/photos
total 368
-rwxr-xr-x  1 www-data www-data   468 Jun 30 13:09 COPYING.txt
-rwxr-xr-x  1 www-data www-data 18092 Jun 30 13:09 LICENSE.txt
-rwxr-xr-x  1 www-data www-data  1937 Jun 30 13:09 README.md
-rwxr-xr-x  1 www-data www-data  1728 Jun 30 13:09 SECURITY.md
drwxr-xr-x  2 www-data www-data  4096 Jun 30 13:09 _data
.
.
... etc.

PHP version: installing Piwigo with php8.1 (retrieved from deb.sury.org repository) yielded identical errors.

Smarty version: installing Smarty5 with Composer yielded identical errors.

Missing files: inspecting the php_include paths (both ./ a.k.a. /var/www/html/photos and /usr/share/php) does not reveal any Smarty files- /var/www/html/photos/include/smarty is empty:

root@mariadb:/var/www/html/photos/include/smarty# ls -a
.  ..

i.e. does not contain "libs/Smarty.class.php" as is apparently expected by the installer. /usr/share/php contains files but no smarty. I did take the steps of separately downloading smarty and adding it manually to the include directories, at which point I received a further error regarding a missing language.class.php. At that point I stopped troubleshooting because the error appears to be beyond my capacity to solve and I couldn't find anything in the documentation about manually installing Smarty, i.e. there is probably something else wrong. It appears that the files are not where the installer expects them, but that seems unlikely considering others have successfully installed Piwigo 14.4.0, i.e. the files were where they are supposed to be.

I do appreciate your reply, if you have any other suggestions I'll be happy to try those too, but it does seem like I'm missing something obvious here, especially w/r/t the missing language.class.php and I don't know enough about Piwigo to continue troubleshooting myself.

Thanks!