Just a guess - we've grown tomatoes outside, never inside. The plant only lasts a year unless the seeds of some fallen fruits regenerate next to the plant. They need to be replaced with new seedlings each year. As the plant gets to the stage of producing new and ripening fruits its productive period has ended. It still produces new shoots and flowers but they don't have the strength to go any further. When the new fruits are forming the advice is to prune out any new growth because they drain away the strength of the fruits. Hope you can understand my ramblings.
My lovely next door neighbour gave me a cherry tomato plant at the beginning of lockdown - I've never grown tomatoes before so this is all new to me. It's in a pot on the kitchen window sill, west facing so it gets sun in the afternoon. However, although tomatoes have grown and ripened, quite a few of the flowers it produces simply drop off. I water it every day - I check it with a soil moisture sensor - and every second day with tomato fertiliser. What am I doing wrong?