A lot is going on with Plasma as the February 2024 closes in.
There will be some leg-work and you should follow the guidance provided by pacman - replace the suggested files with the *5 counterparts.
You may have to temporarily remove packages while syncing the changes to make the system sync.
Especially remove packages build using custom scripts - make notes - you can rebuild later.
Make notes along the way - be warned - there will be more going forward until Plasma 6 is rolled out.
When you are using the Plasma desktop - you will need to be more upfront and keep yourself updated on what is going on.