It's not "boomer FUD". Germany and Japan currently won't listen to you if you say your work is public domain. They only respect copyright expiration and licensing agreements. So if you say your code is PD, and someone in those countries use it, you can still sue them for copyright infringement and possibly win. If you retain copyright and use literally any license then the people using your code have a much stronger defense against you.

You might not care about Germany or Japan, but there's plenty of FOSS developers there that need to have working licenses. Is it possible that those jurisdictions might change their mind? Yes, but it's also unlikely. Copyright harmonization has been entirely focused on the needs of the proprietary world[0]. Thus, if your goal is to effectively disclaim copyright, you need to choose legal actions that fit within the mold that the proprietary world has forced upon us. If the proprietary world does not care about artists being allowed to dedicate works to the public domain, then you won't be able to do so internationally.

[0] e.g.

- Very long copyright terms - Unwaivable moral rights for (copyright-wielding) artists - Strong domestic enforcement for international copyright holders - Upper bounds on exceptions to copyright - Forcing everyone to adopt DMCA 1201 - Making copyright exempt from normal democratic process