Newsflash: Bought a new apartment – sell the old one or rent?

Hi all!First off, wanted to mention I live in Europe.I just recently bought a new apartment in a fantastic location for $400k. $300k of it is a 30-year mortgage $1.8k/mo) at an adjustable-rate of 8.3% – yes, we have had some crazy high rates here for over past 2 years but since it’s an adjustable-rate one so there’s a rather high chance for it to go down over time (fixed rate mortgages are really not a thing here, you can only get one for first 5 years then it switches to an adjustable-rate anyway + it starts at an even higher rate for those 5 years).The current apartment is almost debt free, with only $12k left to pay (at 7.8% rate) and is currently worth $265k – bought it for $180k 2 years ago, mostly with cash and then paid off the rather small mortgage pretty aggressively as I’m not a fan of debt, especially one with such high rate. If I were to rent it, I could probably charge $1k/mo (+ there will def be empty months).On top of it, I have a smaller rental property worth $187k (bought for $90k many years ago) and it’s completely debt-free. I rent it for $750/mo (taxed at 9% rate). So far, had some good experience with tenants but did have 1 empty month in those last 2 years.As for my salary, I take home ~$100k/yr and investments in the last 2-3 years were those properties and SPY.All 3 apartments are in the same, very popular neighbourhood. Real estate prices have been growing pretty fast in the country but even faster in this area, especially after they announced a new tram line to be built in 2-3 years (was just after I bought the 3rd apt) that will make the connection with the city center insanely better.That being said, you can see apt prices are pretty high here but rental costs – not so much because of low avg wages (and you can see how little difference there is between the 1st and 2nd apt, even though 2nd is valued much higher because it’s bigger). At first, it was a no brainer to me to sell the 2nd apartment and then use it to partially pay off the new apt mortgage and use the rest to invest in the stock market (SPY) and/or bonds – so basically unleash that cash and let it work without the hassle of the rental property. Or I must say I definitely appreciated having a peace of mind of not having a high mortgage before that 3rd apt and wanted to keep it that way. However, in most threads I read about similar situations, vast majority of suggestions were to keep the rental property as mortgage is basically “free” money. But it was mostly about really low rates mortgages (like 2-3%), not a crazy 8.3% one. In addition, I’m kind of worried about the stock market being at all time highs when it comes to the moment of pouring more money there + I definitely do notice how the real estate prices have been growing here.That being said, I’m really stuck. From one side, I’d like to get rid of a bigger chunk of the high-rate mortgage for the peace of mind and use the remaining money to invest in SPY and/or bonds + not worry about all the stuff that comes from running a rental (although have been lucky with my 1st apt tenants so far) + regain a peace of mind for if I lose a job. Or maybe buy a smaller rental place for the remaining money. On the other hand, I worry I’ll be losing a really valuable asset that will keep going up in value (and it definitely has been in those last 2 years but I doubt such growth is sustainable) and greatly regret the decision later on.Any advice will be highly appreciated, thank you!