SOLUTION:

1) "Win + I" => Accounts => Other Users => Add someone else to this PC (for example, user without Microsoft account named MSTeams, not Administrator)
2) "Ctrl + Alt + Del" => Switch user
3) Login to second MSTeams user
4) Download and install MSTeams
5) Login to the MSTeams using an account with less activity and close application
6) Ctrl + Alt + Del => Switch user
7) Return to your main account
8) Go to C:\WINDOWS\system32\ and find cmd.exe
9) Click "Shift + Right Mouse" and chose "Run as different user" (find in google how to add it if you don't have this option)
10) Login with MSTeams user
11) Write following command in the console
12) C:\Users\MSTeams\AppData\Local\Microsoft\Teams\Update.exe --processStart "Teams.exe"

To run MSTeams again repeat following steps
8) Go to C:\WINDOWS\system32\ and find cmd.exe
9) Click "Shift + Right Mouse" and chose "Run as different user" (find in google how to add it if you dont have this option)
10) Login with MSTeams user
11) Write following command in the console
12) C:\Users\MSTeams\AppData\Local\Microsoft\Teams\Update.exe --processStart "Teams.exe"

This steps can be optimized by PowerShell script:
#run as admin
if (!([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator")) { Start-Process powershell.exe "-NoProfile -ExecutionPolicy Bypass -File `"$PSCommandPath`"" -Verb RunAs; exit }

$username = '.\MSTeams'
$password = 'YOUR_PASSWORD_OF_THE_MSTEAMS_USER.'

$securePassword = ConvertTo-SecureString $password -AsPlainText -Force
$credential = New-Object System.Management.Automation.PSCredential $username, $securePassword
Start-Process 'C:\Users\MSTeams\AppData\Local\Microsoft\Teams\Update.exe' '--processStart "Teams.exe"' -Credential $credential

Also, you can add this script to the windows scheduler with log in to account trigger with admin permission

Source:

https://techcommunity.microsoft.com/t5/microsoft-teams/solution-microsoft-teams-multiple-accounts-second-account/m-p/548309

https://thomasheinz.net/microsoft-teams-mit-mehreren-accounts-gleichzeitig-nutzen-mehrere-tenants-nutzen-ohne-tenant-switch/