I need to add booking to my website. I stumbled upon cal.com which seemed great. However I've run into 2 issues.

My current options for calendars are Protonmail and cpanel/webmail/roundcube.

cal.com doesn't really work with either of these. For proton its mostly on proton's side, their calendars are read-only externally + a bit buggy: https://github.com/calcom/cal.com/issues/5756

Roundcube uses caldav, and cal.com's support is still in beta with most caldev's being unsupported: https://github.com/calcom/cal.com/issues/3457

Roundcube got me the farthest but the booking emails just don't get sent and the calendar event pops up maybe an hour later + there's 75% the booking just doesn't work. I was told this was the calendars fault 😂.

SO

Are there any selfhosted calendar implementations that support ics feed, external viewing ,etc etc that I can throw on a standard webserver?

Or are there any better foss booking systems?

I just need to book clients and connect it back to a working calendar that's not locked to a desktop. I thought this would be a solved problem in 2026...

I'm not trying to pay for yet ANOTHER software on top of business mail, and a webserver.

Thanks.