Sure maybe You got right, but default Debian 12 package is PHP 8.2 and there is completly no information about issue with default PHP… i was thinking OwnCloud for Debian 12 is PHP 8.2 ready.
The PHP version requirement is listed in the documentation.
Thankfully, the need for PHP 7.4 is easily fulfilled by the DEB.SURY.ORG repos as @tom42 shared.
The Debian that my ownCloud uses is still on version 11 due to no Oracle MySQL repo for Debian 12 yet. (That is tentatively coming in October.) I have been running the DEB.SURY.ORG repos long before I ever upgraded to to Debian 11. I use them as the standard source for PHP on Debian.