Some good advice above. I would say though not to underestimate the fitness you get from all that commuting, even if it is somewhat unstructured. My training used to be really similar to yours - almost identical length of commute that I would do 4-5 days per week for about 5 years, supplemented by longer social or club rides at the weekends. Except I didn’t even have power on my commuter bike, it was a single speed and I basically just went as hard or easy as I felt like. Commuting into London so plenty of stopping and starting, also plenty of people to race when I felt like it! Had no idea about power but did a number of gran fondo/sportive events with good results.
I then got a deal on a Wahoo Kickr that was too good to turn down, first thing I did was a test, came out at 298W, I was 80kg at the time so about 3.7W/kg. I started trying to structure my riding more using HR and RPE from the TR sessions to guide my efforts outside and substituted 1-2 TR sessions per week. Made little to no difference to FTP, I continued to test in the 290-310W range over the next 12 months.
Then I moved cities and jobs, commuting by bike was no longer possible so I got myself a power meter and started making nearly all my riding structured and most of it indoors following TR medium plans (was running and swimming as well as got back into tri). FTP initially dropped simply because the extra structure wasn’t making up for the fact that my total time spent on the bike had basically halved. I ramped up the training as I settled into the new job, and by the time my total training hours (including run and swim) were in the same ballpark as what I used to do when commuting, my FTP was back in the same range as before, with the bonus that I’d dropped to 76kg thanks to the running so my W/kg was nudging above 4.
In February this year I decided to drop the triathlon and focus purely on cycling for a bit. Been following high volume plans with ~2 rides/week being outdoors, usually a long (4+ hours) group ride plus a Wednesday night worlds type session. Total time in the saddle is similar to my commuting days but it is now almost all high quality riding with very few junk miles, and I’m finally making some significant improvement beyond that 290-310W range . Last test was 336W, next one due next week and expecting to get into the 340s based on how workouts have been feeling at 336.
Sorry, this got a lot longer than planned, the TLDR version is that logging high volume consistently week in, week out, can get you to a very good fitness level even with lots of stops and no structure, so don’t be too disappointed if you don’t make big gains by adding in more TR sessions.