Updating PHP only couldn't handled correctly the MySQL upgrade because of the split of the mysql packages (mysql + mysql-libs)
If you want MySQL 5.1.45, you must upgrade it first
yum --enablerepo=remi update mysql
Or, if you want to keep the old MySQL server 5.0.77, install only the client library required by PHP
yum --enablerepo=remi-test install mysqlclient16
Then the PHP Upgrade will work.
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P.S. there is no ffmpeg extension in my repo.
Laptop: Fedora 38 + rpmfusion + remi (SCL only)
x86_64 builder: Fedora 39 + rpmfusion + remi-test
aarch64 builder: RHEL 9 with EPEL
Hosting Server: CentOS 8 Stream with EPEL, rpmfusion, remi