Fix Cypress & a11y tests

[bobvandevijver]

I have disabled these tests with #3530 as they are broken. They need to be investigated and re-enabled.

[macintoshplus]

I worked on fixing the tests of the 5.1 branch.

Some bug fixes are already in PRs. But the most annoying thing is that all the tests were running locally while the result was random with GitHub Action.

Some tests are even dependent on another test to work. Which is a bad practice and generates false failures with the parallelization of tests.