I feel for you, I really do. I find there isn't a lot we as parents can say or do to help.
Sometimes trying to be constructive is wrong and other times being sympathetic is wrong and then there are times when everything/ anything we say is taken as support.
I have 2 DD's eldest settled with 1 DGD.
The youngest is 37 single for a long time. She also has many times when she wishes she could find a partner.
She is a member of a Running Club, work permitting sings in in a couple of Choirs, goes to lots of social events and travels widely. Still no luck.
When I say she travels widely, her Godparents live in the USA and she tries to see them twice a year. She is a Global Quality Manager so lots of business travel - normally. She has even had to travel twice in Lockdown, she wasn't happy but needs must and all that.
She meets lots of people through work and her social life but still after all the time she's been single there's no one. She has tried On-Line dating but that hasn't worked out well and right now she's not doing it.
As for these DD looking at themselves, it never hurts but there are things about ourselves that put other people off that we don't want to change.
I don't know about your DD Pollyj but my DD doesn't want to change her job or her friends but is always looking at ways to "knock the edges off" her words.
There is only so much anyone should have to change before they lose themselves and that would be a move too far.
My DD and some of her friends think it's because they are independent people with homes and money of there own so they would 'Like' a partner rather than 'Need' a partner.
One of DD's friends wanted children so much she had IVF and is successfully and happily a single mum. She owns her house, got all her childcare, and finances sorted such that she works part-time and doesn't get any benefits.
Very brave, I get it, her family are very supportive. She would have liked to be a family with both parents, just like the one she grew up in. However, she said her clock was ticking and at least there wouldn't be any messy Ex if there is a partner in the future.
Having said all that I do feel sad for any singles but thankfully more and more people are finding partners at different times in their lives so we have to keep the faith and stay positive for our children.
Wishing all the single people looking for a partner lots of luck because it seems a certain amount of luck is needed.