First, an increase in memory footprint would not be uncommon going from version to version. Each new version has many new features, bug fixes, etc and some of those changes may come at the expense of higher resource requirements. Also, in 184.108.40.206 database (and plsql) 220.127.116.11 was introduced. Previous versions used 18.104.22.168. Upgrading the db and pl/sql layer always results in an increased footprint for Forms. This has been something we've seen forever.
Second, you provided single values for each version. This does not represent a "memory leak", but rather just an increase in footprint as I described. Further, the issue discussed in the note you referenced was the result of a memory leak in 22.214.171.124 exposed when using OPEN_FORM and/or CALL_FORM. What that means is that memory usage would increase significantly when using OPEN_FORM and even when the opened form was closed, the increased memory would remain rather then coming back down to the earlier usage level.
That issue is not expected to exist in 126.96.36.199. However, if you are experiencing something like this, you will need to contact Oracle Support. Be prepared to provide a test case that can be run by the Support team.
I'm aware that new versions comes with new features and new features requires more memory.
Main problem is that new frmweb process is using more memory than in previous releases and memory is not "cheap" in OCI.
There is no way to increase memory in OCI without increasing numbers of CPU's.
By increasing number of CPU's, you need to buy new processor licence for forms.
I don't want by new licence before i'm 100% sure that there is no problem with memory leak in 188.8.131.52.
There is no statement in note 2618197.1 that bug is resolved in release 184.108.40.206 and note apply's to forms 220.127.116.11 and later.
I think you may have misunderstood my point. The issue mentioned in that note is not reproducible in 18.104.22.168 based on our testing and feedback from the customer who reported it. If you are experiencing a condition that resembles an actual memory leak, as I described it, please contact Support so they can help investigate it and we can get it corrected. Remember that a single data point showing memory use will not be sufficient to suggestion a leak. Support will also want a test case so they and development can reproduce the problem based on your experience.
Regarding CPUs and licensing, you should be able to control the number of CPUs/Cores being used. If you determine that all you need is memory then you could move to a larger shape and limit the CPU usage as needed. The OCI instance may cost slightly more, but at least there won't be additional on-prem licensing associated with it.
Take a look at "taskset" command and others which allow you to control CPU affinity. I have not personally tried anything on this page, but the concepts may be helpful in setting CPU usage. This is NOT an Oracle site.