Apple Timemachine, Synology NAS and Error 45

To make sure I remember:

https://www.synology.com/en-us/knowledgebase/DSM/tutorial/Backup/What_should_I_do_to_fix_the_problem_when_connecting_to_Synology_NAS_using_Time_Machine

(I’m getting more and more annoyed about all things Apple, after having to ditch 2 perfectly well working iMac screens because Apple decided to stop supporting Target Display Mode (TDM).)