Great video and shower leak, a bit similar to your own.

Shows the process of finding leak around and redoing and replacing the drain grate and drain, while also sealing them up again.

He also removes old grout around shower and adding new silicone and grout.

Quick search on shower leaks:

How to fix a tile shower leak without removing tiles - Inspire DIY Kent Thomas [10:53 | Sep 16 2020 | Inspire DIY] youtu.be/g6A91-y-_R4

Short Summary

1. The video discusses the issue of a leaking shower causing water damage, mold, and potential flooring and timber damage.
2. Kent shares his experience of fixing a leaking shower without removing any tiles.
3. He inspects the underside of the shower to identify water damage likely caused by faulty waterproofing membrane.
4. Kent discovers a leak around the waste pipe and proceeds to fix it by removing the drain grate and drain, cleaning out silicone blockages, and replacing the shower pan waste with a new one.
5. Kent trims the plumbing to ensure proper water flow and uses mortar to secure the new shower waste in place.
6. The speaker demonstrates how to properly seal and grout around a shower floor waste to ensure proper drainage.
7. They start by tapping up the bottom of the floor waste to keep it clean for gluing the plumbing later.
8. They apply mortar, ensure it is level with the tiles, and let it set.
9. Next, they glue the pipes into place and remove old silicone and grout.
10. After re-grouting, they share a homemade grout haze remover recipe, apply new silicone around the shower and floor waste, smooth it out, and seal the tiles and grout with a penetrating sealer.