HMRC have announced that they will be sympathetic to people who file their 2019/20 tax return late because of COVID. It is important to notice that they are not agreeing to waive the penalty. All they say is that if you are late, then they will issue a penalty, but they accept that you may be able to appeal on the grounds that you had reasonable excuse (e.g. you had to home school your children) and they will then waive the penalty.
None of the other consequences of late filing will be avoided - interest is payable on tax paid late, the time in which HMRC can challenge the return is extended. If you ask your tax adviser to appeal the penalty then this will take time and so there will be a fee. Unless you file quite soon after the deadline then they could still argue that you did not have reasonable excuse for the longer delay.
It is much better to file the return on time to avoid all these potential problems. In many cases it can be better to file a return on time with estimates and to then amend the return when you are able to provide the correct figure.