Hi,
I was running foreman 2.1.4 on CentOS7. I upgraded to 2.2.0 based on the upgrade instructions:

yum upgrade --assumeyes https://yum.theforeman.org/releases/2.2/el7/x86_64/foreman-release.rpm
yum clean metadata
yum install --assumeyes centos-release-scl-rh foreman-release-scl
yum upgrade --assumeyes centos-release-scl-rh foreman-release-scl
yum clean metadata
yum upgrade --assumeyes tfm\* ruby\* foreman\*

So far so good. Afterwards I checked for the database migrations:

root ~ # foreman-rake db:migrate
API controllers newer than Apipie cache! Run apipie:cache rake task to regenerate cache.
== 20190226182746 CreateRegistrationFacets: migrating =========================
-- create_table(:registration_facets, {})
   -> 0.0254s
== 20190226182746 CreateRegistrationFacets: migrated (0.0255s) ================

== 20200129123555 AddDisabledToUsers: migrating ===============================
-- add_column(:users, :disabled, :boolean, {:default=>false})
   -> 0.0024s
== 20200129123555 AddDisabledToUsers: migrated (0.0026s) ======================

== 20200602155700 DropPuppetRun: migrating ====================================
== 20200602155700 DropPuppetRun: migrated (0.0988s) ===========================

== 20200615071719 AddBmcToSubnet: migrating ===================================
-- add_column(:subnets, :bmc_id, :integer)
   -> 0.0019s
== 20200615071719 AddBmcToSubnet: migrated (0.0565s) ==========================

== 20200616134403 RemoveSettingEnableOrchestration: migrating =================
== 20200616134403 RemoveSettingEnableOrchestration: migrated (0.0025s) ========

== 20200625081552 AddUniqueIndexToLookupValue: migrating ======================
-- add_index(:lookup_values, [:lookup_key_id, :match], {:unique=>true})
   -> 0.0054s
== 20200625081552 AddUniqueIndexToLookupValue: migrated (0.0055s) =============

== 20200630092207 ChangeDefaultVmDeletionSetting: migrating ===================
== 20200630092207 ChangeDefaultVmDeletionSetting: migrated (0.0056s) ==========

== 20200825121733 DropCompareContentHostTemplate: migrating ===================
== 20200825121733 DropCompareContentHostTemplate: migrated (0.2722s) ==========

== 20200918223816 UpdateLoginDelegationDescription: migrating =================
== 20200918223816 UpdateLoginDelegationDescription: migrated (0.0050s) ========

root ~ # 

I executed them again, to ensure they acutally worked:

root ~ # foreman-rake db:migrate
API controllers newer than Apipie cache! Run apipie:cache rake task to regenerate cache.
root ~ #

now the actual tiny issue I saw. I executedthe apipie:cache job as suggested:

root ~ # foreman-rake apipie:cache
2020-11-05 13:05:05 +0100 | Started
2020-11-05 13:05:07 +0100 | Documents loaded...
2020-11-05 13:05:07 +0100 | Processing docs for 
2020-11-05 13:05:25 +0100 | Processing docs for ca
2020-11-05 13:05:41 +0100 | Processing docs for en
2020-11-05 13:05:58 +0100 | Processing docs for es
2020-11-05 13:06:15 +0100 | Processing docs for gl
2020-11-05 13:06:32 +0100 | Processing docs for ja
2020-11-05 13:06:47 +0100 | Processing docs for pl
2020-11-05 13:07:02 +0100 | Processing docs for ru
2020-11-05 13:07:17 +0100 | Processing docs for zh_CN
2020-11-05 13:07:32 +0100 | Processing docs for de
2020-11-05 13:07:46 +0100 | Processing docs for en_GB
2020-11-05 13:08:01 +0100 | Processing docs for fr
2020-11-05 13:08:16 +0100 | Processing docs for it
2020-11-05 13:08:31 +0100 | Processing docs for ko
2020-11-05 13:08:46 +0100 | Processing docs for pt_BR
2020-11-05 13:09:02 +0100 | Processing docs for sv_SE
2020-11-05 13:09:19 +0100 | Processing docs for zh_TW
2020-11-05 13:09:35 +0100 | Processing docs for nl_NL
2020-11-05 13:09:51 +0100 | Processing docs for cs_CZ
2020-11-05 13:10:06 +0100 | Finished
root ~ # 

In the first line with `Processing docs for` it looks like a language is missing? Let me know if this is supposed to look like this or if you need more information.