Folk are under no obligation to include a donation in the will.
https://freewillsmonth.org.uk/?GAds&gclid=EAIaIQobChMIsLvMsfOt5QIVh7PtCh1YpgTqEAAYAyAAEgI-HfD_BwE
"How does the campaign work?
Members of the public aged 55 and over contact one of the firms of solicitors taking part in a Free Wills Month campaign during the designated month to request an appointment.
The solicitor will help to draw up a Will that accurately reflects the wishes of the individual or couple. Those taking up the offer are under no obligation to leave a gift to one of the Free Wills Month charities, however, we earnestly hope that many will see this as a chance to help their favourite cause.
Appointments are limited and are allocated on a first come first served basis. Once all available appointments are booked the campaign will close, this may be before the end of the campaigning month."