Recommended fee for an 100 Euro deposit What is a solid amount of fee for a 100 Euro transaction right now?

I have googled myself but the results were quite confusing to me.

I've had a bad experience with my last payment due to a low fee, so I don't want to go along that road again...
The euro value of the btc transacted does not affect the fee rate at all. What matters is the size in bytes of the raw transaction. Larger size = more fees, and vice versa. 

What decides the size of a transaction? There are a few variables, but for basic transactions what will matter is the number of inputs, and the number of outputs. 

You wallet software may provide a few different 'fee levels' to choose from, or it may allow you to choose a fee rate manually (this should be listed in satoshi/vbyte). At any given moment, the fee rate depends on how many other transactions are being processed, and what their fee rates are.

Think of it as a tour bus that only has room for a certain amount of people, when the demand is higher than there are number of seats, whoever pays most gets to take the bus trip first (where 'taking a trip' = having your tx confirmed in a block). Everyone else who offers to pay less will have to wait for the next trip (the next block, or longer, depending on how far back in the queue they are).

You can check to see what other people are currently willing to pay by looking at a website like Johoe's Mempool. The charts on that page show the number of txs currently in queue, and what the fee rate they are offering is. So to get your transaction confirmed right away, you will need to set a fee rate that is at the top of the chart (right now, it looks like 140+ sat/vbyte will work). Personally, I find looking at the mempool and manually estimating what the fee rate should be works better than the software solutions that just have a couple automatic options (I've tried a few different mobile wallets like this: usually they either give you an estimate that is probably higher than needed, or one so low that I know it won't confirm for days or more).

Keep in mind, if a lot of other people are looking at the graph and also submitting txs right now, there is a chance that what looks like a good fee rate now will not be enough in 10 minutes (because everyone else also sees 140 is the minimum right now, and so they all offer 200. Now your 140 is stuck in line behind them)!