best blu ray authoring software

Mac does not natively support blu-ray, so you not only need software, but hardware as well. The best one I know of is Roxio Toast. You will also need a burner.

https://www.roxio.com/en/products/toast/?x-vehicle=ppc&gclid=EAIaIQobChMI24TDk5Kk9gIVchatBh10mAjbEAAYASAAEgJV8_D_BwE

https://eshop.macsales.com/search/?q=blu-ray&filter.catidpath=2224/2225

I use Toast to create my Blu-Ray home movie DVD's.

I use version 19 but I believe the newest is Toast 20

Bluray takes considerably longer than a regular DVD. 1x means it burns at the same speed as it plays, so the length matters. If it is a one hour movie, it will take at least an hour, longer for bluray. Burning is also a processor/RAM intense process. Do not use the computer for anything else unless you have 16 - 32 GB RAM and a top notch processor and as much free space as your temporary movie files as a minimum; actually 2 x the space is better. Temp files can be as much as 50 - 100 GB for an hour movie. Any of that will slow down the process.

Addendum: does your Mac have an SSD or a spinning hard drive?

Is this yours:

https://everymac.com/systems/apple/imac/specs/imac-core-i5-3.4-21-inch-aluminum-retina-4k-mid-2017-specs.html

You can either have an SSD or a spinning drive - the default for that was a glacially slow 5400 rpm drive. If that is what you have, everything you do is slow, especially something as intense as burning.

Assuming you have the Blu-Ray plug-in the time depends on if you are using a DVD or a Blu-Ray disc. The Blu-Ray disc is faster. Also the drive you have can impact speeds. I recently filmed a wedding that lasted about 45 minutes and it took about 2 hours to burn. I burn many that are only about 300mb and it takes about 20 mins. Also these are my settings under customize:

What issues?

In order to avoid burning coasters, it is best to burn at slow speeds. 1x - 2x.

If it's the default glacially slow 5400 rpm drive, it will be v e r y slow. My estimates were with an slightly older iMac, but a 27" with an i7 processor and a 7200 rpm drive (1/3rd faster).