Tabata et al.[1] found in the mid-1990s that just 2-4 minutes of "high-intensity intermittent training may improve both anaerobic and aerobic energy supplying systems significantly." This was popularized as "Tabata training" 20+ years ago. I generally believe that brief bouts of exercise can be very beneficial, especially because they're easier to do consistently over the long-term vs. more time-consuming routines. For a decade now, I've just been running through my neighborhood most days for 20-30 minutes (with some sprints mixed in) and doing one or two maximal sets of pushups or pullups or barbell exercises at home on a weekly basis. I know a lot of people who got really into longer (e.g. 60-90 minute) gym routines but couldn't sustain it for more than a few months, and then stopped doing anything.
[1] https://journals.lww.com/acsm-msse/Fulltext/1996/10000/Effec...