The appropriate training plan for an individual athlete is probably more complicated than picking the right medicine for an illness. OP should start slow and build up, maybe see his MD for clearance if there is a question there.
Goals vary. Train history varies. The length and intensity of the event varies. Age, genetics, muscle fibre proportions, and the big one is external stress.
I am not thrilled with my personal training this year, averaging a relatively low 12 hours per week peaking at 19 hours in May. Almost all of miles were zone 2 and zone 1 until about June 11 where I added intensity. Two blocks. I gained 5-6% but this also coincided with my long covid and respiratory difficulty easing up. Almost all of the HIIT studies are very short in duration. I am thrilled with 5-6% more power (5 minute) although I usually get 4% but I also do VO2 max intervals year round, but not too often and not too many due to the effect on SNS. My 5 minute power is a little more correlated with volume than intensity and for sure, fractional utilization is volume driven for me. When I am riding 25-30 hours per week for 6-9 months, my FTP is close to 90% whereas now it is just under 80%.
OP...do whatever makes you happy. If you like riding and it is fun, just ride a lot. If it becomes a chore and time is short, add intensity. At some point, you may want to hire a coach to help you sort out what works best for you.