Older monitors were using display panels that only worked properly at their native resolution, trying to use a lower resolution often resulted in blurry fonts. It sounds like macOS is trying to scale your video display and that is going to be a problem with the monitors maximum resolution of 1080p HD (low by todays standards).
You can force macOS to use the monitors maximum native resolution by going to System Preferences -> Displays then hold the Option key while clicking on Scaled. That should give you a list of resolutions where 1920 x 1080 should be at the top of the list. Highlight it and make sure the Refresh Rate is 60Hz. Forcing it to the native 1080p HD @ 60Hz should fix it.
Make sure you have an HDMI 2.0 certified cable, there's a lot of bad cables out there on the market. The LG monitor might have come with an HDMI cable and that one should certainly work. Since it is difficult to know for sure if the HDMI cable you have is a good one, try swapping the cable you have, make sure it's clicked all the way in on back of monitor and on M1 Mac Mini.
If that does not work. Try ordering a USB-C to HDMI cable and make sure it supports 4K UHD @ 60Hz and Thunderbolt 3. That will ensure it's the highest quality. But also something the M1 Mac Min will support. If you ever do replace the monitor this will work for better monitors. This may be more than what is necessary but it's inexpensive. If using a dongle to accomplish this, you would plug the HDMI cable into the dongle and that would also work.
