I have used oven cleaner, Easy-Off, etc, on rental showers/baths that were left really scuzzy. Spray on, wait 5 minutes and scrapped it off with throw-away towels. Follow with a good rinse.
On my personal bath/shower, I use this stuff off Amazon, Wet & Forget. If you start with a clean shower and spray this every 6-7 showers, there's no scrubbing.
www.amazon.com/dp/B0B57SFPQT?ref=ppx_yo2ov_dt_b_fed_asin_title&tag=gransnetforum-21
On a slightly neglected shower, you may need to scrub it off with a sponge. Under regular use, just spray, let sit overnight, and rinse the next day.