Oh I understand. If you do your spring training correctly lowering your winter/indoor FTP will not negatively affect your summer/outdoor FTP and I think this is a good approach.
Ususally what most people see and what is RECOMMENED is when they get to their seasonal peak (2021 peak), then over the winter that drops a little (exact amount depends on many details) and then as you build up your spring volume to previous levels you get back to the same level (2022 peak) and higher if you do things right.
Some people that train harder in the winter and might see a winter increase in FTP. I would even call this “FTP training” meaning you are training to improve your FTP which does not necessarily meaning training to improve your outdoor group or race performance. Thse same people usually don’t see the same large spring increase. They say I increased my FTP by 20w in the winter, but then they don’t improve in the spring or very little also they loose motivation and feel burned out after a hard long winter and a hard spring.
Try to make sure your early winter training does not push you too hard so that you don’t have the motivation to do a hard spring build up period. Holding your FTP is not that critical as it will come back fairly quickly when you do start training harder and get back to previous levels of training.
All this assumes you want a late spring peak period.
Not sure if that helps. Sorry for the slighly off-topic suggestions/thoughts.