Can't change project tempo and time signature without scaling content of MIDI clips.

[Watchful]

I think I understand your statements: but remember that in 4/4 time, the quarter note gets one beat. In 6/8 time, the eighth note gets one beat. So changing your time signature from 4/4 to 6/8 midway through a song should change the tempo of the eighth notes assuming the BPM remains unchanged. So I think Waveform is doing it right from that perspective; you'd need to change the tempo at the point of the time signature change to compensate.

However, you are correct that many pieces need to change time signatures without an overall change in tempo. In those cases, you might consider using a different time signature. For example, in my example, I might change that 6/8 time to 3/4 time to keep the tempo the same: composers do that all the time, which is the source of a lot of argumentation among musicians! "What is the actual time signature of that song?"

[Yulian]

I think I understand your statements: but remember that in 4/4 time, the quarter note gets one beat. In 6/8 time, the eighth note gets one beat. So changing your time signature from 4/4 to 6/8 midway through a song should change the tempo of the eighth notes assuming the BPM remains unchanged.

I apologize for bothering you with my persistence)) Perhaps this is not the most important topic, but thank you for keeping this communication going! =)
In the same MuseScore, changing the number of beats and the note of the beat inside the composition also does not change the speed (I attach the video below), but only changes how many notes can be placed in a bar. It seems to me that this is how it should be. I find confirmation of this in this paragraph of this article:

In Waveform the best way for me would be the ability to separate the speed from the time signature in the same way, as well as the ability to select the note that the BPM value will correspond to. For variability, one could add a "use/don't use time signature as tempo note" checkbox. And if I could still change the beat for the metronome separately, but I beg your pardon, it seems I was already completely dreaming))

So I think Waveform is doing it right from that perspective; you'd need to change the tempo at the point of the time signature change to compensate.

Basically, I think I rarely need to change tempo when I want to change the time signature. But if such a need arose, I could simply correct it with the help of tempo automation.

Objectively now, when working with a project that consists of midi clips, a simple change in the timeline grid, as in my case, causes difficulties that cannot be bypassed.

In any case, with all the nuances, I really like Waveform, I'm very used to it) And I'm very grateful to Tracktion Software for so much work on this DAW. I'm not a programmer, and I can only imagine how long and difficult it is to do. And they give me almost all their works in the form of Waveform Free version! It really deserves a lot of respect!

[Yulian]

For example, in my example, I might change that 6/8 time to 3/4 time to keep the tempo the same: composers do that all the time, which is the source of a lot of argumentation among musicians! "What is the actual time signature of that song?"

Yes, such disputes do sometimes arise realy) Although 6/8 and 3/4 are the same in capacity: both of them can contain 3 quadruple notes and 6 eighth notes)
But still, at the moment in Waveform, even such a change will lead to a double slowdown in midi content. I think this is because in Waveform the BPM values change inversely with note changes in the beat of the time signature.