On pp. 152-3 of Hydon's Symmetry Methods for Differential Equations (2000 ed.), he lists some computer packages for symmetry-finding. This related Mathematica StackExchange question mentions the SYM Mathematica package and Maple's DEtools/symgen. Does SAGE have anything similar for doing symmetry-finding?
I have prepared algorithm in SageMath which finds determining equations for infinitesimals of ODE of order 2 and 3. My paper is published on this with title "Determining equations for infinitesimal transformation of second and third-order ODE using algorithm in open-source SageMath" in Malaya Journal of Matematik. The link for paper is https://www.malayajournal.org/selected_article.php?id=1007
Although not specifically for SAGE (which is a conglomeration of several math packages), Dr. Willy Hereman's "24 [symmetry-finding] software packages" is a continually updated list of software (last updated: March 18, 2020).