Where does the money come from? Religious services are generally funded by donations, and these donations are usually done in the open, whereby (from what I saw) regularly attending and not donating the expected amount would put you in a socially uncomfortable situation.

No reason anyone would would feel social discomfort in my experience, which is mostly in Catholic and Anglican churches, and AFAIK money comes mostly from donations not made in public. I have not felt the least worried about what people would think when I have not had cash on me or about how much I put in.

Depending on the definition of services you are using (e.g. you only mean masses in a Catholic Church, or everything else churches do) lots of things are done without a link to donating: prayers and meditation of other kinds/formats, confession, pastoral care, food banks, religious education and discussion.... In poor countries often things like medical services.

Done the traditional way, no one can really see how much you put in the box and there is no reaction at all from anyone if you put nothing in. Only people right next to you can see anything at all.

Now churches in the UK offer envelopes on which you can write your name and postcode for tax reasons (they can reclaim part of the tax paid on the donation if you are a UK tax payer) so no one can see how much you put in if its in such an envelope.

The definition of a donation is that you don't have to give it.

If you have to pay then it's either a purchase or a tax.

But you know this of course.