Users with this issue in SnapGene 5.1 or later should follow the instructions found here - Windows: Screen Resolution/Scaling Issues.
On some computers with smaller screens SnapGene can get confused and think you have a HighDPI display. Button will be too large and content may have trouble fitting on the screen.
To resolve this issue, quit SnapGene then do the following.

Click in the "Type here to search" box at the lower left of the screen.

Type "env" in the search field, then click "Edit the system environment variables".

Click "Environment Variables..."

In Section "User Variables", click "New..."

Set the "Variable name" to QT_SCALE_FACTOR
and set the "Variable value" to 1.01
.

Ensure the "User variable" is correctly set, then click OK.

Click OK, then quit and restart SnapGene.
IIf the resulting scaling within SnapGene is to large or to small, then repeat the above procedure and set the value to whatever looks best such as 1.1
, 0.9
, or 0.75
, 0.5
etc.