You will be hard pressed to find any low-code platform with a decent calendar. With the introduction of nested list views in retool we have built our own calendar but we only have 3-5 items on each day. Sounds like you would have a much harder time displaying data in the calendar the way we do.
We plan on releasing a public version of this when we have the time but here's a little preview of what we are doing for our scheduling.
I've redacted the events because they have client information but you get the idea. You can click on that little button on the bottom to pop open the event and edit it or move it or mark it as complete.
Unfortunately even with this calendar there are issues. The way retool creates components and sizing we cant effectively fit Saturday and Sunday with a decent amount of space. We are going to add a few more features, like filtering by event type, but it works for us pretty well.