This is a commonly reported issue. The docs say Flow has a max of 250 actions, but performance problems show up with a few dozen. Here's a similar post where the advice was to break flows into multiple flows when there were 50+ actions, with a member of the support team saying they hadn't experienced Flows with 20+ items. Though, the process for creating nested flows is a bit challenging, and involves more of a developer skill-set than what many power users would be comfortable with.