Resolve Database charset issue

We have an issue with Greek characters on our WordPress website. We can enter them in the block editor and they display properly, but when we publish, they convert to question marks.

As far as I have been able to establish, this is related to the character set of some tables in the database not being set to utf8mb4. My understanding is that converting these would fix this issue, which would be a simple job for someone who knows mysql. Obviously if it turned out this did not resolve the issue and additional work was required, this would need to be negotiated separately.