Please help us help you and fill where relevant:
Your LimeSurvey version: 6.1.0_230530
Own server or LimeSurvey hosting: Own server
Survey theme/template: fruity
==================
For personalised invitations to our surveys, we only use the firstname of potential respondents. So far, we have always just used a bogus last name for everyone and simply not used the field in our email templates (fair and easy workaround), but I was wondering: is it actually possible to make this a non-core/non-mandatory attribute? The option to toggle the switch are greyed out.

I agree, actually the only thing that is really necessary is an email address. 

Tammo

I agree, actually the only thing that is really necessary is an email address.

And even an Email address shouldn't necessarily be required. You can use token based surveys for surveys in field in on a tablet or in a central location project.

I usually would create tokens that are given out to interviewers, to have the possibility to restart where they left of if something went wrong with the questionnaire, and also to identify who did the interview. Then you have to put a bogus email address that actually will never be used.

Also, it would be great to be able to export a table with the individual links. Today you need to create your own links in Excel, but it should be easy to export the token links with the token table. But that is a different topic.

Seems we all agree

What's the best way to slide this into the right place? A feature request would seem adequate, but the only place I am aware is bugs.limesurvey.org and there it seems out of place?

bugs.limesurvey.org is the place to make feature requests. Just switch to "feature requests" at the top right corner.