Creating ancient music time signature into the palette

Have you seen the "Early Music features" in the Handbook? - https://musescore.org/en/handbook/3/early-music-features. You can right-click on your 2/1 time signature and then select "Time signature properties". In the "Appearance" section select "Other", then choose the second-last symbol in the drop-down list. Once you have applied it to your staff, you can add it to a palette (assuming you are in a Custom Workspace) using control+shift while dragging it to the palette. Now, if you double-click it in the palette, it will show on every staff. Note, though, that is is just cosmetic, and that you need to start with the correct, normal time signature. To change the appearance experiment with the different fonts in the Format > Style > Page settings.

If you don't like the "backwards" cut C, there is a "normal" one in the "Medieval and Renaissance prolations" in the Symbols section of the Master Palette (to get there, highlight a note or a bar and press "Z"). However, it seems that you have to add it to each staff separately, and play with visibility and the Z axis to get it to show properly.

I hope I have understood you correctly and that this is of some help.