I never quite understood why people say they never looked back, because by mentioning that you used to use DSLR for 40 years, you looked back. By the way, MILC's and DSLR's do the exact same thing, they record digital images. The way they go about it may be different, but in the end the printer or computer screen or monitor used for viewing the images, doesn't really care whether the image was recorded by a DSLR or an MILC. The news companies that have upgraded there equipment have done so because of financial incentives, not because MILC's are better than DSLR's. We're not talking about fine art photography.
I currently own over 20 DSLR's that all work, the oldest of which is a Canon EOS 10D and the newest is a Nikon D850. My very first digital camera, a Sony Mavica that I bought in the spring of 2001, has no reflex mirror which makes it a mirrorless camera. I still have it and it still works. I own several digital cameras that do not have reflex mirrors, which makes them mirrorless cameras. I also own a couple MILC's and have just ordered the new Canon R7. It will take the place of my 90D for wildlife photography, but I will still use the 90D because it's a good camera and it works fine. I own a whole bunch of those light grey with a crimson band Canon EF lenses, and several black ones with the crimson band. Also several Canon EF and EF-S lenses with both gold and silver bands. Plus a couple Tamron SP and Sigma Sport and Contemporary lenses, for both Canon and Nikon. I also own 10 Nikkor lenses. I have some EF-M glass and several Canon, Nikon, Sigma, Tamron and Kenko teleconverters and EF to M and EF to RF adapters. I haven't purchased any RF glass yet, but eventually will.
Bottom line, cameras are tools and toys to me. I've been doing photography for over 50 years and will continue to do so for as long as I can. DSLR, MILC, Bridge, Super Zooms, it doesn't matter to me, as long as they work and I'm happy with the results. I did a job last month at a religious organization that was celebrating their 100th anniversary. There were a couple hundred people there and not one of them asked me if the cameras I was using had mirrors in them. By the way, both cameras did, a Canon 5D mk IV and a Nikon D850. Of the over 500 photos I shot, about 98% were in focus and properly exposed. Not bad for such obsolete technology.