Hi!
For your first issue, it might be that your game does not meet the minimum requirements stated on the download page. If that is the case, please try using the LowSpec version, which you can find on the official Discord server in a post within the #tech-support channel (search for "Low Spec").
If the LowSpec version still has this issue, please make a post reporting the issue in the #tech-support channel of the official Discord server, making sure to specify that you were using the LowSpec version and to include your computer specifications by following the instructions in the #specs-and-saves channel.
For your second issue, you can use the respective number keys (1-3) instead of the function keys.