Saw your comment on MuseScore about no swing mode. I have version 3.3.4.9066, Revision 7684abe and a swing mode is listed (see pg 126 of the associated manual). Indication is that it affects playback mode, but does not have a direct way of notating swing (see below). Not the cleanest, but may be workable:

MuseScore does not have a way to include a triplet in text as a tempo marking, but there is an easy workaround:
1. Add Swing text as described above and make it invisible (shortcut V, or untick "Visible" in the Inspector);
2. Add an appropriate Image of the required tempo marking to the score. These can be downloaded from the bottom of
the "How To" page: How to create a visual swing marking .
3. Resize and reposition the image as required.
Return to straight rhythm
If you want playback to return to straight time after a swing section:
1. Add Swing text to the first note or rest of the "straight" section (see above).
2. Edit the text to indicate a return to straight time: e.g. "Straight."
3. Right-click on the text and select System Text Properties…. Click on the "Swing Settings" tab and set "Swing to "Off."
Apply swing globally
If you wish to apply swing to the whole score, you can do so from the menu: 1. Select Format → Style... → Score.
2. In the "Swing Settings" section, set the desired note value and "swing ratio."

Rich