O&O Shutup Windows 10 helps with the telemetry as far as it can (with Windows 11 doesn't help much due to the lack of telemetry options, which of course doesn't mean the lack of telemetry itself).
Firstly you must check which is the maximum RAM that your processor supports (usually 32 or 64 GB). You can use HWiNFO for this (look at Central Processors>your processor>Memory Ranges>Maximum Physical Address Size.
The only sure way is to not use them at all. There are ways to fight telemetry (e.g. O&O shutup Windows 10 - a helpful program) but you can never be sure that your system isn't "leaking".
Avira is a relatively small in size and light in performance impact antivirus software. The free version doesn't have web protection but there are some browser add-ons (I use Avira Browser Safety with Firefox).