### ClickHouse release v20.12.5.14-stable FIXME as compared to v20.12.4.5-stable

#### Bug Fix
* Backported in [#18166](https://github.com/ClickHouse/ClickHouse/issues/18166): Fix error when query `MODIFY COLUMN ... REMOVE TTL` doesn't actually remove column TTL. [#18130](https://github.com/ClickHouse/ClickHouse/pull/18130) ([alesapin](https://github.com/alesapin)).
* Backported in [#18424](https://github.com/ClickHouse/ClickHouse/issues/18424): Fix possible crashes in aggregate functions with combinator `Distinct`, while using two-level aggregation. Fixes [#17682](https://github.com/ClickHouse/ClickHouse/issues/17682). [#18365](https://github.com/ClickHouse/ClickHouse/pull/18365) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#18428](https://github.com/ClickHouse/ClickHouse/issues/18428): Fix filling table `system.settings_profile_elements`. This PR fixes [#18231](https://github.com/ClickHouse/ClickHouse/issues/18231). [#18379](https://github.com/ClickHouse/ClickHouse/pull/18379) ([Vitaly Baranov](https://github.com/vitlibar)).
* Backported in [#18482](https://github.com/ClickHouse/ClickHouse/issues/18482): Restrict merges from wide to compact parts. In case of vertical merge it led to broken result part. [#18381](https://github.com/ClickHouse/ClickHouse/pull/18381) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#18471](https://github.com/ClickHouse/ClickHouse/issues/18471): Fixed `value is too short` error when executing `toType(...)` functions (`toDate`, `toUInt32`, etc) with argument of type `Nullable(String)`. Now such functions return `NULL` on parsing errors instead of throwing exception. Fixes [#7673](https://github.com/ClickHouse/ClickHouse/issues/7673). [#18445](https://github.com/ClickHouse/ClickHouse/pull/18445) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#18533](https://github.com/ClickHouse/ClickHouse/issues/18533): Proper support for 12AM in `parseDateTimeBestEffort` function. This fixes [#18402](https://github.com/ClickHouse/ClickHouse/issues/18402). [#18449](https://github.com/ClickHouse/ClickHouse/pull/18449) ([vladimir-golovchenko](https://github.com/vladimir-golovchenko)).
* Backported in [#18502](https://github.com/ClickHouse/ClickHouse/issues/18502): Disable write with AIO during merges because it can lead to extremely rare data corruption of primary key columns during merge. [#18481](https://github.com/ClickHouse/ClickHouse/pull/18481) ([alesapin](https://github.com/alesapin)).

#### Build/Testing/Packaging Improvement
* Backported in [#18546](https://github.com/ClickHouse/ClickHouse/issues/18546): Update timezones info to 2020e. [#18531](https://github.com/ClickHouse/ClickHouse/pull/18531) ([alesapin](https://github.com/alesapin)).
