I started this over a year ago and so far I’ve got to the second video of the Introduction. I left it very quickly as just didn’t get it!! I came back to it about 3-4 weeks ago and managed Happy Birthday, just! See Play What You Hear Exercise
I’ve read through the Learn More section for the 3rd video of the Introduction and Justin sums this up perfectly. https://www.justinguitar.com/guitar-lessons/learning-to-sing-for-ear-training-et-003
*1. Find Somewhere Private To Explore your Voice
A lot of singing is confidence, so start somewhere where you can explore singing without your partner or kids sniggering at your attempts. I still have ‘wounds’ from people criticising my singing (and playing for that matter!) that undermine my confidence about doing certain things so I know first hand how hurtful people can be - even if they mean well."
Finding somewhere to do this without interruption is the problem.