@Tcll , you can find any previous version of Opera that you like here: http://ftp.opera.com/ftp/pub/opera/desktop/

I have 16 tabs opened in Opera on my LinuxMint 19.2. I can see that 2 Gb of my RAM is used by system and applications. I think it is not the problem of Opera. Modern web pages are too heavy. That's why they use the large amount of RAM.

@amatczak Thank you! Everything all right now! Forums are working without VPN.

I have the same problem.
traceroute to forums.opera.com (185.26.182.111), 30 hops max, 60 byte packets
1 _gateway (192.168.74.100) 2.584 ms 2.661 ms 2.840 ms
2 94.19.48.1.pool.sknt.ru (94.19.48.1) 5.393 ms 5.744 ms 5.777 ms
3 Router.sknt.ru (93.100.0.22) 4.482 ms 4.691 ms 5.281 ms
4 80-64-103-132.rascom.as20764.net (80.64.103.132) 6.300 ms 6.745 ms 6.732 ms
5 * * *
6 ams-equ-cr1-to-spb.rascom.as20764.net (80.64.96.75) 42.616 ms 35.409 ms 35.627 ms
7 80.249.210.55 (80.249.210.55) 33.272 ms 35.952 ms 36.214 ms
8 * * *
9 n29-03-09-vip.lb.opera.technology (185.26.182.111) 36.940 ms 37.240 ms 34.278 ms
When I type 185.26.182.111 in address bar, I receive the message about wrong certificate. But I can open the login page.
The login page also opens in Firefox, but when I enter my login and password I receive 502 Bad Gateway message.

@daniel130461 , I use Linux Mint 19.1. VPN works fine.

@sgfdhsg , sometimes it is useful to clear browsing data. Navigate to opera://settings/clearBrowserData and check "Content settings" in Advanced tab. This helped me to make Flash working.

@zibi1981 , yes you are right! Chromium's libffmpeg.so is in /usr/lib/chromium-browser.

@sgfdhsg , maybe the problem is not in flash, but in libffmpeg.so? I had something like this two days ago.

@zalex108 , Flash works fine even without any special keys in Windows. But me discuss about Opera for Linux in this thread.

@l33t4opera , thank's for your detailed reply! I'll watch for Opera's behavior.