Zabbix proxy with SQLite does not support Database upgrade, if a major version upgrade occurs. 4.2 - 4.4 - 5.0. That is normal and expected, see the docs:--

https://www.zabbix.com/documentation/current/manual/installation/upgrade/packages/debian_ubuntu

To enhance the administrative experience, Zabbix Proxy should be able to drop/remove the SQLite DB file, as soon as a version mismatch gets detected. Zabbix proxy is already able to detect this mismatch. The file becomes obsolete as soon as the version mismatch is happening.

Instead of the admin manually deleting that file, Zabbix proxy should do that.

There was also a proposal in the Telegram group, that Zabbix Proxy should also delete the SQLite DB file, as soon as it detects other problems besides a version mismatch. That could be a further enhancement.