In general you need not update to the newest ("vanilla") TeX live if you are happy with your current TeX system. Many packages in the TeX world have been stable for years (the popular citation package
natbib for example has not been changed since 2010), some others will only have received carefully crafted, small fixes for very specific bugs.
But there is a number of actively developed packages that get updated substantially from time to time (
polyglossia, ...). If you use one of those packages very extensively, it may be useful to keep your system up to date.
It might be important to note that the TeX world as a whole is not stationary. There are occasions where some new (sometimes big) development comes along. Davislor points out that TeX live 2020 comes with HarfBuzz support for LuaLaTeX: That is a big deal for many people who write in non-western scripts.
So you don't have to update. Many people are perfectly happy with older TeX live versions (in particular the TeX live from the Ubuntu repositories). But if you want to use new features, you will have to make sure to regularly update your system.
Considering that some Ubuntu LTS versions are supported for five years and they usually get an updated TeX live (nominally) from the year before they are released, a TeX live 2019 from July 2019 is not too bad in spring 2020.
It is perfectly possible to have several versions of vanilla TeX live installed in parallel, since they go into different folders. You can then switch between them by adjusting your PATH variable accordingly. (MacTeX for macOS even has a nice GUI for that.) In theory it should also be possible to install vanilla TeX live alongside your system TeX live, but then it might be more tricky to keep your paths in order. (I don't think I know of anyone who has vanilla TeX live alongside a system-installed TeX live, but I know of many people who have many TeX live installs from different years.)
If you run an update, there is always the risk that you may run into compatibility issues. Generally, my advice would therefore be not to update or upgrade close to an important deadline. But more often than not updates have no or only very small (and easily fixable) impact. Of course the occasional bug or backwards incompatible change sneaks in. Bugs are usually reported and fixed quickly, so if you find anything don't hesitate to contact the developers. For backwards incompatible changes authors usually suggest workarounds and are happy to help with the transition.
If you want to update, don't let the possibility that there might be some issues scare you. Make sure you have a bit of time to test and sort everything out.
It is a good idea to clear the auxiliary/temporary files (
.toc, ...) for your document after an update. Those files are written by specific package versions and a package update might mean that a different format is expected. Usually problems with the auxiliary files produce very strange looking errors, but they are easily resolved by deleting the auxiliary files and recompiling.
For your specific case of
apa7 and 7th edition APA style, I think the best choice is to upgrade to TeX live 2020 and keep it updated as long as that is feasible (deadlines permitting).
apa7 was only recently added to TeX live and was not part of TeX live in July 2019. This means you would have to install the class manually. Manual installations are always a bit tricky, because you are then responsible to manually check and updated all dependencies as well.
And this is not a theoretical concern.
apa7 does not implement citations and bibliographies in APA style. Instead it recommends to use
biblatex and specifically
biblatex-apa is one of the most complete implementations of APA citations and bibliography style in the TeX world. When the 7th edition of the APA manual was released,
biblatex-apa switched from implementing 6th edition APA style to 7th edition. That is to say versions of
biblatex-apa from before November 2020 (versions below v9.0) implement 6th edition APA style, versions from after November 2020 (v9.0 and above) implement 7th edition APA style. (6th edition APA style is still available from
biblatex-apa6.) This means that you also need to update
biblatex-apa when you manually install
apa7 to get citations and bibliography formatted as expected. But
biblatex-apa depends on
biblatex and Biber. A current version of
biblatex-apa should be run together with
biblatex v3.14 and Biber v2.14 (released in December 2019). So you will have to update those two as well. This is considerable effort.
Here it seems much, much better to just install the current vanilla TeX live 2020. Then
biblatex and Biber will or can be installed in matching (current) versions.
biblatex-apafor the bibliography. Old versions of
biblatex-apaimplement the bibliography and citation style from the 6th edition of the manual. Only versions of
biblatex-apareleased after 2019-11-23 (v9.0) implement the 7th edition style (the 6th edition style is available in
biblatex-apa6). In theory it might be possibly to only install
biblatex-apa, but if your
biblatexis too old you might end up having to manually update
biblatex, Biber and all its dependencies as well.
apa7delegates the bibliography formatting to
biblatex-apa(an independent package/style). Depending on your version of
biblatex-apayou will get 6th or 7th edition APA style (basically whichever was the current version when you installed
biblatex-apa). Yes, when you have vanilla TeX live it is straightforward to keep the system up to date (see tex.stackexchange.com/q/55437/35864). But keep in mind that TeX live still requires yearly 'upgrades' that should be performed via new installation.
.bcf, ...) and recompile from scratch. Maybe the problem just occurs because of a leftover auxiliary file that was written with different package versions. If that doesn't help: Ask a new question with MWE (see link) and upload the complete
.logfile to a text-sharing website.