I recently switched to Mint Linux.  I installed the Minecraft launcher via the Software Manager and it loads fine.  When I try downloading Forge though, Linux complains about it being an executable from an unrecognized source and tells me to try getting it from the Software Manager instead.  Forge isn't listed there though. ?  Any other Linux Minecraft players out there who can help a newb?  I'd hate to have to reboot into Windows every time I want to play Minecraft.

Thank you.  That was very helpful.  I did that and it worked.  For any other newbs, don't forget to make sure you're running that command from the same directory as the .jar file.  For example, if you've put the jar file on your Desktop, you need to run "cd Desktop" from the terminal before running the "java -jar forge-1.15.1-30.0.41-installer.jar" command in terminal. I forgot that step and was wondering why Java couldn't find the jar file when I was looking at it on the screen! ?