I've been looking into and testing different time tracking software. After I switched to Centiga.no for billing and accounting, I also switched to Clockify for tracking hours spent on different projects and clients, and it works well. (I can export CSV and create the reports needed.)
The only thing I'm missing in the free version, is the ability to easily mark hours/entries as billed/finished. (Invoicing is a premium feature, and so is bulk editing.)

So, searching a bit, I found many alternatives. Most cheap or free options has some of the features I want hidden (only available in expensive plans).

For me, the most important is that it should be really quick to (re)start a timer for some project. This is easy in Clockify, but also seems I found a promising alternatives:
1. TMetric. Seems to have better reporting, easy way to bulk set entries to Invoiced and more. It seems the paid features are stuff I don't need. (Disclaimer: The trial period hasn't ended, so can't yet be 100 % sure if the functionality I've used is available on the free plan.) Support was responsive. Only drawback I found, was no native dark mode.
2. Futuramo also seemed very promising. It has dark mode, and most features I wanted. Haven't tested it too much yet, as I think I like TMetric's time entry options even better, so giving that a shot first.

I could also mention actiTIME, which also seems to perform well. The approach is a bit different, and entering time a bit less flexible (but it also has other possibilities, maybe a better fit for some).

My plan was also to give InvoiceNinja a shot. I did look in the hosted version, but there the reporting module is a part of a paid plan, and I haven't gotten around to installing a self-hosted version yet.

Will see how much more I'll end up testing. If TMetrics keeps working great after the trial period ends, I will probably stick with that.
(I know Centiga.no is planning for a paid module for time tracking, so I might give that a try, though. Direct integration with billing and account would be nice.)

There are quite a few others to check.
(Wasn't sure if General was the correct category.)