Steps to reproduce the issue

Update a clean 3.10-dev to 4.0-dev nightly.

Login to backend and check the error alert which is shown.

Then goto "System - Information Database" and check the tooltip shown when hovering over the "One Problem" badge for the CMS.

Expected result

After login to backend, only the usual error is shown:
.

In "System - Information Database", only the errors marked with a green frame in the 2nd image in section "Actual result" are shown, but not the one marked with the red frame in the same image.

Actual result

After login to backend, not only the usual error is shown:
.

In "System - Information Database":
.

The errors marked with the green frame are not related to this issue here, they belong to issue #28530 and will be solved when the changes from my PR #28501 will be merged up into 4.0-dev.

The error about database not having been converted to utf8mb4 marked with the red frame is related to this issue here, see section "Additional comments" below for the explanation.

System information (as much as possible)

Happens only with MySQL or MariaDB.

Additional comments

The problems comes from recent changes for the utf8mb4 conversion (PR #28495 ) having been merged up into 3.10-dev already but not yet into 4.0-dev.

The changes in 3.10-dev not being in 4 yet make the utf8mb4 conversion run when doing the update, which should not be the case of course. And this then unmasks other errors which haven't been noticed before and which will be fixed with my PR #28515 (or a new later PR as replacement for that). And so the unneccesary utf8mb4 conversion fails, and the database checker shows this as an error.

So this issue is just for documentation of the issue, the fix is already on the way.

I only wait for the changes from staging being merged up. Alternatively, if that takes too long, I can do the same changes here in 4.0-dev. but this will then cause merge conflicts later for the merge up.

@wilsonge Let me know what you prefer: Wait for your merge, or fix it in J4 and cause later merge conflicts for you (but in that case I will help to solve them if necessary, of course).