Inazuma is a bit different than Genshin Impact's other nations Mondstadt and Liyue. While some features like donating to the statue of the seven stay the same, the way you spend electro sigils greatly differs. Electro sigils are donated to the Sacred Sakura Tree, but once you max it out, you'll need to take your business elsewhere.
The electro sigil shop will be closed when you arrive in Inazuma City, and won't open unless you meet very specific criteria. You must reach level 50 at the Sacred Sakure Tree to unlock the shop. That means that you need to find and donate 1250 electro sigils before the shop will open.
Once this task is complete and you claim your rewards, Netsuke no Gen Crafts in Inazuma City will open. This shop carries some rare furniture items, weapon ascension materials, and has a mora exchange. You will need to get a high-completion rating on all islands to unlock this though and open hundreds of chests.
The cost of single items in the shop is much lower than the 25 electro sigils that the Sacred Sakura Tree required, so it should be much easier to empty out the shop.
For more Genshin Impact content, check out How to use the Secret Room Key in Enkanomiya in Genshin Impact on Pro Game Guides.