How to correctly handle a multicurrency bank account?

I am not used to invest and my understanding of taxation and economics is quite basic, if I am misunderstanding something please be patient. I apologize for my oversimplified or incorrect language.

I am a European citizen and when I opened my bank account in Japan I was given a standard account and a separate multi currency one (CITY/PRESTIA). I would like to verify if I understood correctly how things are supposed to work to avoid mistakes I probably already did and I am quite confused by my situation.

1. A multicurrency account is not insured like a "normal" bank account and it is a sort of "investment fund" that the bank handle like a real bank account for certain operations.

2. I can use the money in my multicurrency account in Japan if 1) I convert it in Yen and 2) MOVE it on my "real" bank account so I can cash it from an ATM or wire it to another Japanese bank account. Until the money is in the multicurrency account I do not have to care about "capital gains" (hope the term is used correctly) even if temporary converted in yen, but the moment I move those yen in my REAL bank account they will be counted and there could be tax implications.

3. When I had to close my bank account abroad PRESTIA told me to wire my savings from my former account abroad to my multicurrency account coordinates directly in the foreign currency and I have done it twice some years ago. I had one transaction wired in EUR (<10M yen) and the last residual transaction (few 1000s EUR) was wired and converted in JPY at the time.

3.1 My understanding is that savings are not subjected to taxation as stated here multiple times.

3.2 The transaction from my former bank abroad deposited in yen in my multicurrency account is not going to generate any kind of capital gains so even if I were to move that amount into my normal account I have no particular obligations.

3.3 The transaction from my former bank abroad still in EUR could generate capital gains depending on EUR JPY rate, but I need to record the rate when I convert it in JPY, and when I decide to cash that money I may have to declare the realized gains.

3.4 If I convert the money from 3.3 in JPY, but let it sit in the multicurrency for years like that or buy another currency I have no obligation as the gain / loss are not yet realized. Still better to remember what the conversion rate was.

4 I tried to lookup on the web, but since I am quite illiterate in economics my understanding of the quote below is limited. I would like to understand if moving from the multicurrency account to my normal account the equivalent of 200k JPY or less in capital gains every year could be exempted from a separate tax declaration.

為替差益が生じても確定申告が不要な場合とは

為替差益が生じたからといって必ずしも確定申告が必要なわけではありません。

具体的にどのような場合に確定申告が不要なのか解説します。

なお、確定申告が不要な場合も住民税の申告は必要となるため、注意しましょう。

給与所得・年金所得以外の所得の合計額が20万円以下

年収2,000万円以下の給与所得者で、為替差益を含めた給与所得以外の所得が年間20万円以下の場合、確定申告は不要です。［注5］

https://www.smbc.co.jp/kojin/money-viva/gaikayokin/0003/

4.1 I am employed in Japan with my company dealing with 年末調整 and never did a 確定申告 before, how do I proceed? I see the link in point 4 has a time schedule

Thank you in advance for your time and sorry again for my potentially poor explanation.