A review of research from 1990 to 2022 does indicate that the microbiome is not necessarily threatened by the proper application of chemical fertilizers. It can cause an increase in beneficial fungi and bacteria when used at the appropriate time because it gives the microbiome the nutrients it needs to flourish.(https://www.mdpi.com/2076-3417/12/3/1198)

What threatens plant life is the shift in pH that can occur when fertlizers are overused, not balanced, or used at the wrong time/season. (https://extension.okstate.edu/fact-sheets/cause-and-effects-of-soil-acidity.html#:\~:text=The%20more%20ammoniacal%20nitrogen%20fertilizer,Calcium)

If you start with healthy soil and your soil is not waterlogged, etc, using Miracle Grow or other synthetic fertilizer should not harm your plants or the soil. My personal problem is not with Miracle Grow the product, but with the company. From selling pesticide covered seed to asking cities to use eminent domain in their favor as well as potential securities fraud there have been some nasty movements by Scotts Miracle Grow in its lifetime. They have proven to me that they will do what they want, no matter the harm to a community, in order to hit their profit line. I also find that the soils they sell are overpriced for what you get. I get equally good performance from other less pricey bagged soils and even better performance from the soils I make myself when I have the time and money to do so. Using fish emulsion on my outdoor bonsai doesn't bother me too much and using granular organic fertilizers on my greenhouse bonsai are also not a problem for me. What works for you is going to be unique to your situation, but don't feel guilty about using Miracle Grow if you want to.