I take a different approach to this since I was emulating a lightweight PRM/CRM on my system I was kinda porting over from emacs org-mode. I’d love a way to pre-warn for specific dates like you can get in org-mode though (so, say a recurring bday date would ping you say 2 weeks or a month in advance in some sort of query).
So, I have a template and create a page for every person since I often link to them by name when in meeting or need to have a task assigned to them and track it later (I have a large team).
So, the template looks a bit like this for our mythical friend Jack Sparrow:
Jack Sparrow
- Tags: #rm #work #piracy
- Ping: #2021w36 (this would be the week I need to reconnect with them - have a query)
- Full Name: Jack Sparrow
- Meta
- Email:
- Phone: +65 xxxx xxxx
- WhatsApp: +65 xxxx xxxx
- Telegram:
- Twitter:
- Company: Black Pearl Trading Co
- Role: Captain
- Location: High seas
- TODO Birthday: Xxx ddth, yyyy
DEADLINE: <yyyy-mm-dd Ddd +1y> - Anniversary: –
- How We Met
- In a harbourfront dive bar in Batavia… er, Jakarta [[Aug 21st, 1689]]
If I talk to them on a specific day, I just refer to them by name and that shows up in their page as a contact and what we might have talked about or done. Tis very handy.
It doesn’t solve the “warning” part of the reminder about the birthday but I’ve actually got a couple of queries in the advanced querying section to figure out a way to get a list of “Birthdays and anniversaries in Next Month” kind of thing.
Would that kinda work for you? (though I am still puzzling out the query… 
Logseq querying is kinda tough (tho I guess not really worse than emacs).